first choice - ethel's suggestion see if you can get a freebie
if not - decide on a router either by price (linksys or netgear are pretty sound) - or better look in a few pc mags - see what's recommended
hit google, kelkoo amazon and just get the bet price you can (remember the postage)
if it's just one machine - and they are both upstairs - I'd still say use wire (I just don't like wireless!)
54 is the optimum (for now) - your broadband max is 8Mb - and unlikely to get above 24Mb/s anytime soon - so no problem.
however if you ever get another machine and want to share files - you will realise how bad wireless actually is