Win7 Laptop can't see XP computers

This problem seems fairly common. One person fixed it like this.
Tried all of the above using win 7 with live mail. Set the default app for .doc to wordpad when into live mail and opened an email with .doc attachement. Then went back and set the default app back to ms word. Boom done problem solved. I think this whole thing started when i removed ms works.

You can get there by typing "default programs" into start/search window and hitting enter.

Okay, that's cool, I can use Microsoft Works to view my .docs, but the other problem is more serious - can't install any programs due to the Error 5: Access is Denied". I've been poking around in all the Users/account settings, and my account is still set for administrator privileges, but something is definitely wrong. I probably need to get into a different part of the forum for this question!

Just a quick follow-up. Got some assistance on the general forum with my issue opening .doc files and installing programs. Was able to do a System Restore back a few days. Looks like the problem was the new firewall (beta version!) I recently installed. All is well now. Thanks again, folks!