You cant really answer that its diffrent from everyone. The best way is to slowly increase your clock by small increments, test for stability (recommend 3dmark03, 05, doom3, farcry, hl2), if you get threw all those then your pretty stable, keep an eye on temps, and keep turning it up until apps start crashing or you stop seeing a positive or worthwhile increase in 3dmark, then turn it back a few and youve found your optimum clock, reapeat all these steps with a bunch of diffrent drivers and find the optimum drivers and that will really make your system smile.
Remember to use driver and cab cleaner though.
If you want some help overclocking step by step feel free to pm me and we can talk more. Download coolbits from guru3d.com to enable overclocking (the new nvidia drivers arnt good for overclocking at all, so if you plan on oc'in, definetly plan on finding diffrent drivers). Guru3d also has TONS of drivers, lots of good posts there to on walkthrews / tutorials / and just plain old good information.
Asus p4c800 Deluxe,1 Gig Mushkin PC3200 Dual Channel Level II V2,Pentium 4 3.0 512k 800fsb HT, Thermaltake Xaser III, Thermaltake Spark 7+, Sound Blaster Audigy2 ZS Platinum Pro, eVGA GeForce 6800 GT