strange frame rate, please help

Hi, I’ve had this frame rate related problem for years, but now it’s become important that I fix it. Whenever I run certain OpenGL programs (game or screensaver), the frame rate never goes higher than 19fps. Before you go any further with your suggestions, here are my system specs:

AMD Athlon XP 1600+
256MB PC2100 Crucial RAM
64MB All-In-Wonder Radeon 8500DV (Catalyst 02.3)
Windows 98SE
SB Live! Value

I’ve run Quake 3, Return to Castle Wolfenstein, and the cool water screensaver from Moore Chaos at 150 fps and beyond, and yet, some programs never run higher than 19fps. For instance, everyone who has Windows has the 3D Text screensaver. That only runs at 19 fps, including the flower box, 3d pipes, etc. I usually didn’t care that much, but now I have Jedi Knight II and it tops out at 19fps, unless I run in windowed mode and alt-tab away and back to the game, then it runs at 80fps at 1600x1200 and 32-bit color. If I load a game (or quickload), it returns to 10fps. A simple alt-tab returns it to its nice 80fps.

I can’t figure out where this problem stems from. I’ve tried different drivers, different resolutions (from 640x480 to 1600x1200) and changing my desktop resolution and color depth as well, but it never goes faster than 19fps. I don’t think it’s the video card or CPU power, but then again, I also have never had anything but AMD processors. I also used to have this problem with my old 16MB nVidia Riva TNT, so it’s not solely ATI’s fault. Has anyone ever had this weird framerate problem? Please help.