lunchtimecinema...
the type of thing you are envisioning has already been done. (well not exactly what your are planning) ... but I remember having seen standalone arduino projects which recieve input via twitter. you may want to search the exhibit part of this forum and check out how other people went about it. (or go ask google...)
again, the way I would tackle it, is getting everything working via usb. Once you have that, you can move on to wifi or bluetooth. I would recommend WiFi over bluetooth. Xbee is probably the easyest solution, however if your goal is to design a consumer product I find Xbee sort of unelegent (though thats just a personal bias...) ... if you are just building this for yourself or a friend and just want a proof of concept, Xbee is probably the way to go...
cheers
p.