Something like this?
When you say "control my pc" I assume you mean get the files off it to play? If you actually want to remote control your PC you'll need something more like a PC hooked up to the TV i.e. a media center or something of that nature.
If you just want to play downloaded video/music files then the above should do it, you'd need wireless capability on your PC upstairs also (or wired if you wanted to run a cable down).