First, some background. I am one of the developers of improvements to the recently-opened source code to Bungie's Marathon 2 engine (for more, check out http://source.bungie.org).
And recently, I have been adding OpenGL support to it, utilizing the engine's visibility, transformations, and clipping calculation. However, I'm now having problems with some of the textures. The wall textures work perfectly, but the landscape textures often look bizarre, and the sprite textures are often mangled in various ways (Marathon has rather Doom-like geometry).
For example, one of them is missing every second scanline and has part of one of the wall textures appended to it.
What might be causing this misbehavior?
For the record, here's what I have:
PowerTower Pro 250 (604e; 160 MB RAM)
ATI Rage Orion (Rage 128; 16 MB VRAM)
Apple OpenGL 1.1.2
Also, OpenGL is running in windowed mode instead of full-screen mode, because some of the Marathon-engine display is 2D rendered (HUD, overhead map, terminals).