Question: Is there a way to find out, using Win2008 R2 Hyper-V manager or a command-line tool, the externally-accessible IP Address(es) of Windows XP Hyper-V guests? 

I'd like to be able to connect to my guests by IP address via Remote Desktop (for cases where name resolution is not working properly) but without combing through the DHCP server it's been challenging to know which IP address corresponds to which host. 

Any ideas?

Assigning static IPs to each guest is possible but is something I'd like to avoid.

Answer: 
look at this link it will do what you want 

<http://blogs.technet.com/b/m2/archive/2010/07/29/how-to-get-the-ip-address-of-a-virtual-machine-from-hyper-v.aspx>
Why not just use the Hyper-V Manager to open the VM's Console? It works remotely if you have Remote Management enabled in the Firewall Settings, and you don't have to do any look-ups in the DHCP Server. Otherwise, no, Hyper-V does not track it's VMs IPs, just their MAC addresses.