Yes, in most cases ( no pun intended) If the power supply conforms to the ATX standard then it will fit.
also you get what you pay for. If you find a 500W PS for $30. It is either not a real 500W PS or it will not last.
Be prepared to spend around 80-100 on a 450W PS
Also Antec makes some of the best power supplies around.
Also a side note. If you can afford a UPS (uninterruptible power supply) get one. Don't be fooled into thinking a surge protector will be the best protection for that new power supply and PC. A surge protector will not stop a Voltage sag. This will be passed on to your PS and cause it to fail. A UPS will provide a constant power along with surge protection.
OK, enough of my work bleeding into my personal life.
Check out
http://www.apc.com for all your UPS and Surge protector needs.
( sorry but our stock is in the tank and we need to move some of this stuff biggrin: )