The best solution is to uninstall Avast and stop the hangs.
On top of that, you should consider repairing your Outlook after you have uninstalled Avast.
1. Go to
:\Program Files\Microsoft Office\Office12\SCANPST.exe to repair your PST folder. Your pst file should be contained at C:\Documents and Settings\ \Local Settings\Application Data\Microsoft\Outlook\Outlook.pst. Repairing PST takes several minutes.
2. Next, run Microsoft Office Diagnostics to repair Office issues. You can find this application at Microsoft Office Tools start menu.
3. Run MS Outlook, you should see that your outlook will not grind your harddisk after these operations.