First of all, I want to say thanks to Blind Nero, I read your posts and your suggestions made me able to actually play beyond the Cyclops attack in Chapter 1. However, I'm still having issues with the game and cannot even load Chapter 4. I'm going to copy and paste what I've posted on the Steam forums so far:

Relevant info:
The first error was Internal driver error in IDirect3DDevice9:: present(). I followed the advice from here, but was unable to fix it.

The next many crashes were all The Instruction at 0x####### referenced memory at 0x#######. The memory could not be 'read'. I followed the advice from here , but was still unable to fix it. In fact, setting +mat_forcehardwaresync 0 caused my whole computer to crash.

Specs:
Windows XP SP3, all windows updates current to today
DX9.0c all patches current to the release this month
Radeon HD4830 using the 9.3 catalyst drivers from this month
Motherboard chipset and onboard audio drivers are current
2GB Ram
AMD 64 x2 6000+, with the processor driver and dual core optimizer installed.

I've got everything I can think of patched to current, my game still crashes when I close background processes and when I leave them, it crashes with Catalyst AI disabled or on, and with my pagefile at 2GB and 4GB. I've verified the cache files twice and rebooted countless times. I don't have a problem playing other Source engine games at all (including Left 4 Dead, which I would imagine is much more power hungry than Dark Messiah), and have no issues running more demanding games like Oblivion, The Witcher, Mass Effect, etc.

Anyone have any suggestions I can try to fix this? The only thing I can think of to try beyond what I've done is that I only installed the Single Player version of Dark Messiah. I'm not totally sure that installing the Multi Player version would fix the problem, but I'd be willing to try it.

Disabled audio acceleration as per a suggestion on the ubisoft forums I saw and got a new error: failed to lock vertex buffer in CMeshDX8::LockVertexBuffer

Post 2:
Ahahaha. It figures that as soon as I make a topic I find a solution. Apparently the game sometimes has problems detecting the correct level of Direct X, so I just started my game up with the -dxlevel 91 launch option and it's been working so far

Hopefully I don't run into more problems with the game.

Post 3:
Guess it's not totally fixed. I got up to the tower on the roof of the mansion right at the start of the game and it crashed again with the Internal driver error in IDirect3DDevice9 message. :\

There was also a report that popped up asking if I would send a message to microsoft, saying that the module affected was datacache.dll

Any ideas at all?

Post 4:
I cannot load Chapter 4. Each time I try it crashes and and says that there was an error with the datacache.dll module.

Upgraded to the new 9.4 Catalyst drivers and have been able to play further in the game, but it still keeps crashing. Any ideas about what I can do to prevent these crashes?