Interesting , but the Original textures and things will not get any clearer at higher resolutions . The most noticeable difference is in the 'anti-aliasing' qualities of the large resolutions .
You should notice that the higher resolutions produce much smoother edges on the character models ( most noteably LAra ) and other edge type tid bitsin the same way that running AA ( anti aliasing ) will on the lower resolutions .
using an older ATI card ( 9000 ) the images looks very smooth and clean if I run it at 640x480 with at least 4x AA , but the image quality is superior if I run with aa off at a resolution of 1600x1200 .
Try downloading gambits texture pak ( http://www.resonantedge.com/trx/?p=download ) and running at a couple of test resolutions using the new textures . Higher resoutions should produce more clarity and less moire' and other low res pattern distortions.
if this doesn't work you have some other weirdness , like possibly glidos not being able to load and runnign soem default vesa mode .In one of the other threads Paul ( Mr. Glidos) describes what to check for if this is the case .