you adjust the multiplier if you can (amd's after week 39 or 339 or w/e are locked) to the highest it can go and then adjust the FSB accordingly
The clock speed will be the multiplier x front side bus
UPDATE:
decided to oc my 4200 more so my 8800 gts would be able to reach higher fps'
I got to 2662 MHZ with a 100% load on both cores at 66 C max which is decent since 73 is terminal temperature, leaving the proccesor on 24/7 will probably overheat, but I don't so thats ok. The VCORE is at 1.420
I tried going to 2706 MHZ with a 1.420 VCORE, but it gets an error in the PRIME95 torture test so I raised the VCORE to 1.450 but then I got the BSOD when it reached 30 seconds into max temperature so I backed it down a bit
I use the Scythe Ninja Plus Rev. B heatsink with the stock 120 mm fa which runs a 1200 RPM, so you can probably get a bit better then me
hmm lets see, its been awhile since i have had that cpu in my box...
well, the HTT was 250 with multi at 11.
the HT multi was at x4.
the ram was probably set to ddr2 667 in bios, maybe ddr2 533 for stability testing.
i know my vcore wasnt over 1.45, i had to run it at 1.525 to reach 2.9 though (and boot at least). you are probably right about having to up the voltage.
i have a zalman 9500.
your temps are awefully high. When I had my 4400x2 air cooled on a Zalman CNPS9500 I was able to clock it to 2.86ghz and temps never were above 55c or so. This was on 1.5vcore if I remember correctly.