Hey guys, looking for a way to get the username of a user on a remote computer on a network of WinXP machines, anyone know how?

Basically my plan is scan my class room to get everyones usernames, and then when I get net send spammed I'll know who it came from.

I've had a try of a few examples on here, but I'm not 100% sure if they're what I'm after.
http://vbnet.mvps.org/index.html?code/network/


Thanks inadvance.