I just did some more tests, this time with a Voodoo3 2000 PCI 16mb card. I ran Redguard, and I saw texture problems mentioned previously in this post. So I applied the "voodoo 3 fix" mentioned earlier in this post. It worked! I then tested 4 resolutions -

640x480, 800x600, 1024x768 -all worked.

1280x1024 did not work however - it defaulted back to 640x480 resolution.