Cannot connect to multiple networks

I'm having a strange problem that I hope someone here can suggest some possible solutions to...

My laptop runs Vista 32-bit, SP2. I am trying to connect to two networks at the same time - one, a dial-up connection to the Internet, and the other a wireless connection to my router here at home. Both connections work fine if the other is not active. If I try to connect to both, the computer appears to connect to both networks, but I am unable to print to a print server on the wireless network as long as I am connected to the Internet via the dial-up connection. If I disconnect from the dial-up connection, then restart the wireless connection, I can connect to the print server just fine.

I do have a firewall installed (COMODO, v4.1), but I don't think it's a factor because even if I disable it, the problem does not go away.

I have read an article on Microsoft's site (http://preview.tinyurl.com/2d297or) about configuring default gateways only on the public connection (which in this case would be the dial-up connection), but I've tinkered with that and it didn't seem to help.

Can anyone else out there suggest something else I might try? This is bugging the hell out of me because it seems like it oughta just work.

both should work ok. what devices on the wireless network can you see via "network and sharing center-tasks-view computers and devices"