When importing, what items do I get to keep and how? Any answers, keeping BG1 spoilers to a minimum would be appreciated.

Well in short, you get to keep almost nothing. You sort of get to keep a certain helm (but IIRC that's in the starting dungeon of BG2 regardless) Also if you manage to get an item called the golden pantaloons you get to keep them, but only if you manage to find them again in the starting BG2 dungeon.

Alternately, there is a trick to keep all of your main characters gear by hitting pause at the right time...

Lame though ;)

Really Dace? Elaborate please...

while the load screen is displayed hit space. when the game starts you will have a black screen and no controls and the game is in pause. press H to display the controls and select your character you can now remove all gear and drop them of as long as they are not cursed (e.g. claw of kazgaroth is irrevocably lost). After Jonny's jadajada you pick the gear up.
Not sure if this is what Dace is talking about, but I suspect it is.
There is also a mod that will allow you to keep the gear.

I am split on this issue. I think you ought to keep more of your gear or at LEAST have a chance to buy it in the Mart. The claim that "you may find some items for sale along the way" is a red herring.
Regardless you should find replacements for most BG1 items soon enough except
Cloak of Balduran
Claw of Kazgaroth
Scimitar +5
Scimitar +3
Chainmail +4
Chainmail +3
Platemail +3
all of which you should not be able to (or attempt to) import.

SPOILER
>
>
>
>
>
>
>
Actually, if you have the Claw on you when you import (and not the Helm), then the Claw will be in the same spot as the Helm is found (replacing the Helm). Personally, I'd rather have the Helm, but I just thought I'd bring that up.

Most importantly, you lose your party members. No matter who was in your group for the final battle of BG1, BG2 starts out exactly the same way: The game assumes that your BG1 party was you, Minsc, Dynaheir, Khalid, Jaheira, and Imoen.

Next off, if your PC is a Mage or Bard, all of your spells are erased from your spellbook. Don't fret: You get to choose them (or better ones) during Character Creation in BG2, and you'll find plenty of scrolls to replace them with soon enough. In addition, successfully scribing scrolls earns you EXP points now.

Finally, all characters will have their items (even those classified as Cursed) removed from them. Again, don't fret--you'll find replacements for most of your favorite gear. Also, the game can also detect certain items that your PC was wearing at the end of BG1: Some of these items, if worn, can then be found in BG2. I have only seen this to be the case with one item, the Claw of Kazgaroth, which otherwise does not exist in BG2. Importing the Claw, however, is not a wise move, since it appears in place of a very good Helmet, and the Helm is much better than the Claw.

The only noteworthy items that you will not find again are:
Algernon's Cloak
Claw of Kazgaroth
Horn of Kazgaroth
And the following BG1 items are obtainable using mods:
Cloak of Balduran (Tactics)
Kiel's Helmet (Tactics)
Kiel's Morningstar (Tactics)
Kiel's Buckler (Tactics and also Rogue Rebalancing)
Dagger of Venom (R.R.)
Spider's Bane (Tactics and R.R.)
Silver Dagger--Werebane (R.R.)

I have always liked the Claw. It's cursed alright, but it does wonders to most saving throws and gives a +1 AC bonus. The helm of Balduran is easily replaced with one of many helms in the game, whereas the unique properties of the Claw allows you to wear a certain cloak while retaining most of the benefits from a Cloak of Displacement. I have found the Claw, but I presumed it was either coincidental or class related. It did not strike me to open BG1 and compare the characters.
My shortlist was merely equipment that I recon it will take a long time to replace. I have not tried to acquire the scimitars in BG2, but someone whispered that they will be replaced with inferior models (+2) if you try. I find it remarkable that you can get better scimitars in BG1 than in BG2.
Kiels buckler is nice with an elven thief in BG1, especially with a one handed missile weapon. I find the +1 buckler in BG2 a suitable replacement until UAI allows all shields to be used. Since you can waltz straight in and grab it in Athkatla I don't regard it as irreplacable.
One other thing though - it is also impossible to get the original sword of balduran (longsword +1, +4 vs lycanthropes) if I am not mistaken. It would be nice to have against certain greater werethingies.

Would you be able to import-drop a scroll of dimension door? A spell I sorely miss.

This is a little off-topic, but the thing that sucks when transferring a character over is that your NPC's proficiencies are so drastically changed.

I always switch around some of Minsc's proficiencies when I use him.

Interesting in that a class not involving a fighter type with 18 constitution can essentially wear the Claw of Kazgaroth without ill effect.

The claw will lower my HP with a single exception (a 19 cons necromancer) so for me it is a choice between having more HP and taking damage and having less HP and avoid damage. It is especially good on mages in BG1 where it hinders missile fire from disrupting spells.
AC is interesting in that a little can have a large effect. If the enemy must roll 10 or above -1 to AC is practically without effect, but if it must roll 19 it means a lot - changing the probability of being hit from 1/10 to 1/20. This makes even marginal improvements in AC desirable.
The eternal question is whether it is better to concentrate AC in one char or spread it around. It would depend on if the enemy is mixed or uniform groups I 'spose.

To bring this back on track - are there any items that will replace the helm apart from the claw?

On the material side, I'd say that the Buckler+1 can't hold a candle to Kiel's Buckler: Kiel's already is +1 for any character with a DEX in the 14-17 range, and is extremely important for Dualed Thieves (of which BG2 has no shortage), who need that precious extra point of DEX to boost the Thieving skills that they can't point points in any more.

But what really irks me is the way that BioWare jacked all the Bucklers in general: There are three classes (Thief, Bard, Druid) that are restricted to Bucklers, and yet instead of creating more decent Bucklers to sprinkle around the game, they decided to delete the only BG1 Buckler that was any good. And on <u>top</u> of reducing the Buckler selection to the +1 enchantment, they put only one Buckler in the entire game.
Rather unbalanced, when you look at the Sentinel / Fortress / Reflection / Harmony / Saving Grace / Dragon Scale / Balduran side of the equation.

Thankfully, Rogue Rebalancing rectifies this. Bucklers of up to +3 enchantment are available, Kiel's is back, and new custom Bucklers for Thieves, Druids, and (sort of) Bards. Yay!