1. Directly in the soft/game, e.g. in Quake3 type "r_swapinterval 0" in the console.
With Quake2 engine games, I think it's "gl_swapinterval 0"
2. With drivers.
Starting from the official 1.05 release /I thinnk), you can disable v_sync for Opengl/Glide.
I got the unoffical 1.07.95 set, they are supposed to allow disabling in Direct3D.
3. Other tweaking software.
V3 Overclocker for example. Never worked for me though.
Main rig: Athlon64 x2 4200+ | Asrock 939N68PV-GLAN | 4x512MB PC3200 | 120GB Seagate | Samsung DVDRW SH-S203D | VX550W PSU | WinXP Home SP3 / Ubuntu 7.10
Headache generator: K6-2 500 | FIC VA503+ | 2x64MB PC133 | Voodoo 3 2000 PCI | SB32 ISA PnP | 15,2MB IBM | Xubuntu 8.04 / DeLiLinux 0.7.2
Lappy: Compaq EVO N115 | Mobile Duron 1GHz | 384MB PC133 | VIA KM133 | Xubuntu 8.04
A big thanks to MS's Vista for making me look into Linux distros!