I got a amd xp1900+ 512 ddr geforce 3 ti500 and my frames go from 100 to fuckign 14 sometimes.. it's not your system man.. this game is fucked up.. www.suckatana.com
In your Video preferences, set texture detail to medium. I had the same problem, the game would run smooth as silk most of the time, but slow to a crawl when entering a new area.
I'm running at 1024 with everything maxed and this fixed everything for me. No more lag - at all.
Hope this helps.
Finally!!! I removed my Soundblaster Live! card and know I'm getting on avg about 45 FPS (min-low 20s on Omaha Beach; max-90s indoors, no action). I'm pumped, though I wish I could get better.
Not sure what the problem is with the SB, but I noticed that every 7 seconds or so my framerate would drop to around 5, then cycle up to as high as the 90s. I don't care, just so I can actually play now.
Another tweak (although my crkced-out mobo wont allow it) is to make sure you AGP apeture size is set high enough (try 128MB if you have 256MB of RAM). I am getting REALLY bad FPS but my memory sharing is only set to 12MB, and MY BIOS won't let me change it. but your probably will . . .