Sue,
I am not convinced that your problem is actually caused by Avast but perhaps by something resulting from the removal of the Norton software.
Just on the off chance - Can you open IE7, click on tools/internet options/Security. If the "reset all zones to default level" is NOT greyed out, click on it to reset all of the zones back to the default settings and see whether that makes any difference to your problem.
If that doesn't work, the only suggestion I can make at the moment is to go into Outlook, find an existing email that you can't print using the network printer and see if you can print it to a local printer. As a last resort, if you haven't kept a copy of the avast install file, download one, then uninstall Avast, reboot and repeat the print test in Outlook - you should be able to do this without going on line.
If the fault is still present when avast has been completely removed, then it would confirm that we should be looking else where. If it isn't, then reinstall Avast and some more head scratching will have to take place.
And finally one other question - is the office network one where all of the computers and the network printer are connected to the LAN ports of a router that has its WAN port connected to a broadband modem, or is the router connected to a dedicated server?