Meh just get what you think feels right, you'll probably want an nVidia card, probably 8800+, and I perfer intel processors. I also suggest, if you have spare money, alienware. If not, probably a dell or toshiba will do it.
EDIT: The firebird thing looks like it has pretty good specs, might wanna overclock the processor a bit though even if it is quad-core.
I was also thinking about getting something off of eBay, bad idea?
Yes. Anything you get on ebay will be secondhand crap. Even if it says 'new' in capitals.