Wireless home network problem.

I have set up (?) a wireless network between my office computer O.S. Win XP Pro, my laptop O.S. Win Me and a remote desktop O.S. Win Me.
I managed to get my laptop to connect to the office machine and share the internet connection. Shut down computer and next day, found that my office computer was not able to receive e-mails, even though the internet connection was ok. Any ideas for a REAL newbie?
TIA.