Here’s what I would do:
First check to see if you have NetBIOS enabled. (Enabled, not automatic!).
If that doesn’t clear up the problem:
Try adding the 2 computers to the Domain AND Workgroup (of same name). You can visit this site: <http://www.windowsnetworking.com/articles_tutorials/wxpjoind.html> for a walkthrough.
If that doesn’t work, try:
Hooking the computers up to a print server, then having a connection from each computer to the server (this way any computer can print on any printer at any time).
You may also want to standardize everything (I consider this the best solution):
Get XP Pro on all systems. Add them all to the same DOMAIN. Get a print server.