ADVICE?

I have sucessfully run rDesktop on my N810 to my Win XP pro PC from within my house using the IP address of the PC through my wireless USB router. (It's spotty but mostly connects). However I have never been able to connect at another access point (it locks yp on the OK button and finally times out). I'm guessing the IP address is incorrect in the rDesktop start screen although I got it using http://whatismyipaddress.com/. I have RR cable for ISP. Any ideas anyone? Thanks!