I have attempted to talk to everybody I can think of and cant find anyone to mark my map...

<font color=silver>Welcome to IW, Durning! [img]graemlins/happywave.gif[/img]

What stage of the game are you presently at? You can only get access to the Dorn's Deep area by completing the previous chapter which involves completing a quest in the Severed Hand complex. Once that is completed, a character there will mark your map and you will have access to Dorn's Deep.</font>

I have found 3 of the machinery parts for the astrolab... I need to get some seeds in order to get the fourth piece. I have heard that these can be found in Dorns Deep but I can not get there.

<font color=silver>The seeds are for a different quest -- the restoration of the arboretum and have nothing to do with the fourth astrolabe piece. All four pieces can be found within the Severed Hand. Only after you have all four pieces will you be able to finish the chapter and move on to Dorn's Deep.</font>

That last piece is a bugger to find.

SPOILER
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Its on the first floor, but can only be reached from an elevator on the 3rd. Enemies in that sector are much tougher than the rest of the first floor. Theres one large shadow in particular that drops some nice armour.

If you have this one the rest are:

from kaylessa
from the priestess
from the war-room in the north tower