A P4 with SDRAM? Ouch
I have 2 AMD Athlon XP 2000 systems. One uses SDRAM and a Voodoo 5 card. The SDRAM system, High FPS is 60-70 (in tower)...get into the game, smoke, etc, mean average is 30 to 40. The other system, with DDR RAM, GeForce 4 4600 (and some mild overclocking) shows 75 fps everywhere..tower, smoke, etc. Cant seem to go higher due to monitor refresh (60hz)
My thought is your motherboard/ram is your bottleneck. If 4x AGP is enabled and everything else the guys mentioned is checked, I'd really consider a new motherboard that takes advantage of the CPU. SDRAM, as I mentioned, is much slower. You should be able to find some P4 DDR or RAMBUS boards.
Good luck