Xander,
Splurge a little and go for a case with a 400 watt (350 minimum) power supply. Especially if you want to overclock, I'd be suspicious of a case AND PS for $30. I just priced out a new system (wont get one till the new thunderbird procs come out) for gaming, and a good airtight case and separate PS came out to just over 100--though I spent more on the case than I needed.
Hmmm