This is another widely debated topic. Theres a lot of people using 20pin PSU's in the DFI boards that require 24 pins....I figure as long as you aren't running SLI'd GPUs and things like that itll be fine. Dude at Xtremesystem Oppainter I believe it is has a 3GHz overclock, 6800Ultra and crap like that and runs with a 20pin PSU, but yeah an adapter would work.
If you don't know how to change the multiplier Grim, you REALLY need to read more up on overclocking and get familiar with your BIOS before you go buying expensive *** RAM, a whole new setup, and expecting to OC like nothing.
AMD64's are slightly more complicated than Socket A systems when it comes to overclocking and the thing that is the most annoying on these forums is when people ask questions about overclocking that are really easily answered by the most basic of common sense and guidelines of overclocking.....most of those time those people just dive in without truly reading what it's all about and what's involved.
Time and time again I've seen questions about voltages and stability and just otherwise really simplistic questions that wouldn't even needed to be asked had they done reading and research.
Anywho, sorry for the rant