I'll try to help the best I know. First off stay away from the units that have a dvd player built into the receiver, asking for problems. Get a unit with a stand alone receiver. I also wouldn't reccomend Sony, they have special connections for their speakers so you can't upgrade them if you choose to do so in the future. You want something with lots of connections so that you can add on as necessary. The 2 that come to mind with a stand alone receiver and plenty of connections are Yamaha and Onkyo. WorstBuy carries Yamaha and Circuit City carries Onkyo. Go in and take a look, if you can stretch your budget another $50 Circuit City has the Onkyo s790 on sale for $409 in this weeks flyer.
I'm not sure about connecting your pc, I guess it depends on the type of connection on your video and sound card. Just make sure the receiver you pick has extra connections of the same type. If all else fails look around on the site, there are plenty of threads about budget systems. You just don't want to get something you can't upgrade down the road. Hope this helps some.