I am on the same type of dynamic DSL Ip's that you are on... I did find something that was a little more useful... go to:

http://www.deerfield.com

and download dns2go.... it allows your computer to map a dynamic IP to a static name... and on limewire since you can enter names and numbers for Ip's you just type in the name and go to town it's all free to (if your using a subdomain of dns2go.com) I realize that it's a little overblown for solving the gnutella problem but I thought it might be useful if you want to set up any sort of servers in the future...

as for the linksys thing... I found that linksys is a little flakey on high port numbers... if you want to have gnutella work nicely you may want to forward the ports on a lower number... say less than 1000.