Make note that the wrt54 model of linksys was a "lemon", in that it had firmware problems that the company never bothered to fix (yes most of their other devices are of the highest quality!) As WW suggested, at least port forward is the best bet. The WRT otherwise gives unreliable performance, dropping out unexpectantly, etc. To find out more, see WRT654G listed under UPnP heading > Linksys, part of way down this page -> Connection problems? Check here first! (click on link)

Also be sure you configured your firewall to allow LW full access: Windows Firewall - LimeWire