In regards to the OP Question without throwing out the Get a Mac line.
How old is the PC? What are the Specs of said PC? And How much did you pay for the PC?
All this factors in on whether or not you dump money into a PSU or not.
Also, your symptom isn't 100% indicative of a PSU issue. Bad Ram can cause this to happen as well as Faulty wires, and just recently I had an 8800 GTX video card in my PC cause a similar issue.
Let me know what your working with and I'll let you know if it's time to upgrade.
Mike