<< If you are running an Athlon greater than 800 MHz, you must use a 300watt P/S. The 250 won't have enough current on the +5volts side for the Motherboard. >>
I'm not sure that's always true. I am able to run my classic athlon at 1gig and I have two hard drives, cd, cdr, bunch of fans, geforce, zip, etc....
It all depends on your power supply and system. There is no definite answer whether it will run or not. Just try it and be sure to check everything else such as seating the cpu, video card, memory before you replace your PS.