|"Is there a guide that says what motherboard goes with what video card, etc?"|
Yeah, it's called computing.net...lol
"I put the specs from the top computer into newegg and it still came to around $500"
I don't see how you could even do that? The specs are incomplete. No motherboard, no CPU model number, no RAM speed listed, no power supply. The 9500GT is not a good gaming card, you'll have to do better than that or you'll be disappointed. And you don't need a separate sound 'card'...onboard sound is pretty darn good these days.
You don't have an OS disc you can use? Windows 7 will add $100-200 to the cost depending on the version. Do you know anyone in college? The student version is about $30 ;-)