The WRT54GS is very simular to the WRT54GL the only main difference being with the WRT54GL you can get unofficall firmwares that add features where quite often with the WRT54GS you cannot.
This is because the L is based on Linux and has slightly more Flash memory (the memory that holds the firmware)
the S is based on Vxworks and has a smaller Flash.
But based on the questions you've asked I'd expect that you maybe wouldn't be intesrested in playing around with the firmware and therefore the wrt54GS should do the job nicely.
Edit:
It might be worth checking which broadband package your one as I noticed some are now being offerd with "Free wireless router" so if your luckly you might be able to get one out of virgin
From other threads here I think it's a Netgear they are sending out so should be a fairly decent router.
http://allyours.virginmedia.com/webs...ervice.do?id=2