Oh, sorry I didn't read your post right. You're buying a computer complete, not building one your self.
On that note, Cyberpower is just fine, I've heard good things about them. When you're looking at computers from them, you want to make sure you get a 64 bit system, atleast 4GB of ram, and an Intil i5 or i7 processor. The Intel i-series processors are simply amazing, and I would advise against getting an AMD system at the moment - but don't get me wrong, I love AMD and they make good stuff... Intel just has the upper hand with the i-series at the moment.
What I said about power supplies and video cards is still valid though. The only reason you'd need 750W is if you were going to SLI or Crossfire your video cards. And I don't recommend doing that unless you have the money to burn. I have 2 ATI 4870's in crossfire on my system and it's not much of a performance increase. Looks cool though.