Remote desktop in XP Pro ? Alternate DNS server ?

I want to log onto a friends computer with the remote desktop in XP Pro. I have had a practice on my own local network to see if all went ok and it did. I logged on with IP address, user name and password. How can i get my friend to give me his ip as i a bit confused at this point. Do i use something like this http://www.ipaddresslocation.org/ which will read his IP then he gives it to me. Just not sure as, doest his ISP change his IP now and again ? Was easy on mine as i have created static IPs on my computer
Scroll down half way on that page and it says
My IP Address
XX.XX.XX.XXX
Also when setting up a static IP you need preferred DNS server and Alternate DNS server. The preferred DNS server i can get but where do you get the Alternate DNS server, is it something to do with your router
Thanks for you time DOJ Harris