Hmm...
GTA3 (so far) runs mostly only in the following Config :
- intel CPU
- the older V1.03.00 Driver
This is the only Configuration I know works for most Users (still, there are remaining issues for some).
You would have to look for a x-3dfx release of that time, that carries the same Direct3D Core (which seems the key to success, I
believe the V1.07.00beta has it, but I don't exactly remember)
Patience did an internal list of Drivers containing it though (at that time, I think she listed 3 Drivers in total)
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So far, I haven't seen a complete, centralized Document describing all existing Workaround (if present) for Problems in GTA3.
For NWN, (since you already got it running), you can unfortunately only test things yourself...
The only hint that might help, would be to go through some of the existing Help Pages found in the Links Section of the Archive.
I know many Forums and Webpages have
really good Info on how to improve things on various Games; but of course this as good as it gets, the burden of detail Testing remains with you and your specific Config in the End...
The new Mesa based approach I haven't seen in Action, so I don't know how well it will perform. But looking at the goals, this is definitely something to try when it comes to problematic OpenGL Games
3D Analyzer hasn't progressed alot in OpenGL as far as I know, but it is always worth a shot to test something new.
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A fully installed AmigaMerlin Driver should be listed as such in the Device Manager, and of course you should see the fully functional 3dfx Tools.
If any of that is missing, try rolling back to "Standard VGA", then deleting the 3dfx Files from the Windows\System Directory, as well as the 3dfx-.inf from the Windows\Inf Directory. Finally, manually delete the 3dfx entries from the Registry. After this procedure, the System should be clean of any 3dfx Files, and be ready for a clean-as-possible new Driver Installation