My basic instinct with this issue is that unless you want a very long ethernet cable running from your Xp Computer to your Vista Computer, I would definitely go wireless.
Certainley with Virgin Media Cable broadband you should have no connectivity problems.
The equipment that you will need consist of :-
A Wireless Router to replace your Webstar modem, A NIC PCI Card ( but I suspect the Xp will already have one installed). A fast ethernet cable and a wireless adapter or wireless PCI card for the Vista. ( Making sure that the adapter or card are Vista compatable).