It's the potion of perception that increases INT and DEX both by three. Potion of agility just sets your DEX to 18. BUT I believe you'll lose spells when your INT goes back down to normal.

No you don't. The only things intelligence is used for is to: determine how many spells per spell level you can put in your spell book, and to determine your chance of scribing a scroll into your spell book. In the PnP game, it also determines what level of spell you can cast (i.e. need 18 intelligence to cast level 9 spells), but in this game only the above two things are what intelligence does for your wizard. It does absolutely nothing involving how many spell slots you get, nor has any other effect on your spellcasting. Also, once a spell is scribed into your book, it won't leave your book, regardless of your intelligence. Thus, you could have a wizard with a 9 intelligence, and just use potions of genius when scribing spells. It will work the same as if you had an 18 intelligence.

Potion of Genius: +4 to INT
Potion of Mind Focusing: +3 to INT, +3 to DEX
Potion of Agility: DEX set to 18
Potion of Perception: +20% bonus to Find Traps, Open Locks, Pick Pockets, and Stealth

The stupidest Mage in the world can use Potions to get a 150% chance to successfully scribe every single scroll in the game, and the spells will stay in his spellbook after the potions wear off. Also, the restriction on allowable spell levels (which does not come into effect in BG1, only in BG2) only applies to the main character Wizard. By this I mean: If you create a Mage with 16 INT, he or she will only be able to learn spells up to and including Level 8. You can never scribe 9th level scrolls (without raising your INT), because you simply aren't smart enough. Now, NPC Mages do not have this limitation--they can scribe spells of any level they want.

Thaks a lot for all your help and for the welcome. I found out it was the intelligence that kept me from learning the spells, but since I'm fairly far into the game, I guess I'll just have to forget about it.

Thanks again you guys