I don't think I am totally clear on what you are doing, but I think you want to remotely gather IP addresses from usernames?

Depending on your naming convention this may or may not work. There is a system call in Windows called nbtstat.

You can do nbtstat -a 'computername'   (without the quotes)
You can do nbtstat -A 'IP ADDRESS' (without the quotes)
[download]

This will return the name of the logged in user and maybe you could parse this into something useable? I don't know how you could do the parsing without perl though? And of course, if the users name is not the computername, my whole theory falls apart on you.