The WRT54G's were a lemon due to a major firmware problem which Linksys never bothered to fully repair. Two options ... one if get a 3rd party fix for the firmware which is NOT recommended for the technologically ignorant. Else, to at least port forward the device which will at least reduce the problems faced. For port forwarding, the first & most important step is setting up a static ip; Static ip for Vista (click blue link).

Then the next step is setting up the router's NAT firewall rules: PortForward.com - Free Help Setting up Your Router or Firewall & find your model on the list.

Also you will need to set firewall rules for your software firewall; Windows live one care User Cant Connect - LimeWire

And these are things that will aid your solutions: (a) Problems with the search, __ (b) Hostiles List