What kind of settings do you have on that? Since I play for the purpose of winning I tend to have every on what I call "mush" settings. Basically, everything turned down. I get about 40-50 fps on my machine. Try upping your memory to about 128mb on your onboard. Turn on low quality sound as you have an onboard sound card. Don't have Hardware sound or the other types of hardware sound features (3D positional).
It is the fact you have onboard sound + onboard video which is killing your FPS, if you don't turn these to a minimum. BTW, the GF4 is an MX onboard, so that is a DX7 type chip, which doesn't help at all. I don't think there is a GF4 Ti (DX 8) onboard version.
Lastly, are you complaining about poor fps because you aren't getting 100fps like in Quake 3? People seem to equate poor fps if their fps isn't above 60.