Originally Posted by Rills 
Update: I was correct on the Direct X. My video card is DirectX 10 and this game set it back to 9c!
There are ca. 25 different versions of Direct X 9c. It's updated quite often. It's possible a few components needed for Drakensang are not shipped in the standard redistributable Direct X package.
Direct X 10 does not work under XP, AFAIR. Direct X 9c is the maximum.
Unfortunately this is really a problem where we can't do much.