4850 Weird bad shadows

Hey

I'm new to this forum, but I hope any of you can help me with this one.
I 'm brazilian, and already checked some brazilian sites but I didn't got aswers for this problem.
The issue is that in some games (50%) the shadows are very deformated, pixelated and with some other great bugs.
It kinda let me down coz I went from a 6800XT that had no such errors.
I know my system is bottlenecking the GPU (P4 3.2 HT P2M, D101GGC, 2Gb DDR400 Single channel, HDs Sata2 @ Sata1, WinXP) but this is no reason for me to get these kind of problems...
I'm using cat 8.6 + hotfix and I strongly think that upgrading won't help.
I'll upload some SS


Dirt when I activate shadow mask. The shadows are all in diagonal


Trackmania United Forever bugs incredibly when I activate the highest shadows


Yet another disappointment with Lock On. When highest shadows are active, the selected aircraft doesn't have shadows at all


The highest image quality possible, and yet, look at this...


I manage to disable the shadows mask but now I got pixelated shadows in DiRT.

I'm really starting to give up on this and get back to my 6800
Is there something that I can do to improve this shame or this is simply the way that my last gen ATi card handles shadows?!?

Yes, upgrade to the 8.8 drivers and when 8.9 comes out upgrade to that!