A good TNT2 Ultra card ( i Have a Diamond Viper V770) would fit that rig. You may want to check out the hardware forumn for previous questions or advice.
I currently have a PII 333, 256PC100&133sdram, fly with 1024X768 resolution, 32 bit mode and with the Viper II (32mb) I get FPS in the high 30's/40's untill I get around A1, alot of clouds or alot of smoke at a damaged base. Then it drops down into the lower 20's or if there are alot of planes and smoke lower still. I abbreviate my horizon view in those cases (shift f1, f2, f3) and I'm ok. From what I understand a TnT2 ultra should give you good performance when used with up to a 600mhz cpu. After that the cpu isn't the bottle neck, the video card is.
-Westy
[This message has been edited by Westy (edited 11-16-2000).]