There is instructions at msdn that can be found easy:
http://msdn.microsoft.com/en-us/library/bs2bkwxc(VS.80).aspx
To start Mscorcfg.msc tool go to:
Control Panel\Administrative Tools\Microsoft .NET Framework 2.0 Configuration
Microsoft gives instruction to setup new trusted zone for every project location at intranet. There is better solution if your corporate intranet protected by firewall and you have many project locations (or location can change frequently: like with ClearCase).
Instead of URL select Zone for code group condition type and select Local Intranet zone.
Select FullTrust permission set at next page. Finish the wizard.
Viola: All intranet is trusted. The only thing: you should be sure that you can trust your intranet :)