One thing you'll probably want to do regardless of whether or not you get the printing issue sorted out, and that is turn off sharing on the network (unless for some reason you and your husband need to share files across the network). Also, I'm guessing the thing that is popping up on his computer is the messenger service (VERY different from MSN messenger the chat program that everyone uses). The messenger that I'm talking about is a little tool that receives messages broadcast over a network from other microsoft OS'ed computers. It's not useful in any way on a home network.
Right click on the My Computer icon (either on the desktop or in the start menu) and then click on manage in the list that pops up. Be very careful in the screen you are now in. It's a management console for your computer and you can get at some very low-level stuff in here that you can't get at in other ways. (not meant to scare you!! It's safe to use this tool... just don't go changing things willy-nilly).
Find the Services and Applications section in this window on the left hand side and click the plus sign beside it so that it opens up and you can see the Services area. Click on Services and you'll see a list of all the services running on your machine on the right hand side.
Find Messenger in that list and double click it. On the screen that pops up, choose disabled in the Startup Type dropdown list. Then click stop and finally click ok. Close the computer management window.
Do this on both computers, and you won't get annoying random popups from the other computer on your home network.
ps. here's a link to a page at Microsoft that talks about this: http://www.microsoft.com/windowsxp/pro/using/howto/communicate/stopspam.asp