Don't waste your money on a piece of crap router buy a linksys save yourself some headach's, Before the dlink fan boys bash me they do make pretty good stuff but linksys is the best.. As far as the wireless card goes you can mix and match them (it will just default to the lower speed) I suggest going wireless G so if you transfer files over a home network its alot faster, but wireless b works fine as well it will give you full internet speed but slower ethernet speed. and usb wireless adaptor's work very well as well and you don't have to add a card.
But I have to say this as well if it isn't a laptop why bother, All wireless networks can be cracked and people can steal your bandwidth and gain access to your network. If it is at all possable to run a wire to the desktop then do it that way a good wired router are only about $20 and no one can get on your network.