If I am using a laptop connected to the WRT54G, I need to use http://172.20.0.101:<port> to access the RT's GUI (remote administration I guess is what it's called). If I had a laptop connected to the RT (which I will never do since it's not wireless), I'm sure that the IP you provided will work.
The admin/admin won't work (any longer). I changed the password.
My setup is done (for now). I put the RT in the DMZ for it to stay online (port range forwarding wasn't enough apparently).
A lot of (my) confusion was because of my boneheadedness of reseting the RT early in the process, which wiped out the provisioning string required for VOIPo. I think I had the setup done right early on, but it wasn't getting Phone 1 lit, so I kept changing settings hoping it would work, which resulted in lots of questions here.
-Craig
Bookmarks