Symantec Management Platform (Notification Server)

Using SMP7.  When you retire a computer will it remove itself from the Manage|Computers|All Computers view?  If so how long does it take?

Retired assets will continue to appear here, since they exist as resources.  This is showing all resources, so they will never disappear.  You must delete an asset (removing all historical data associated with it) if you want it to disappear as a resource (and therefore not appear in the resource list).

Will it remove it from certain reports like "All Windows 2000/XP/2003/Vista/2008/7 Computers with no Agent"?

Retirement is going to pull the resource out of vComputer, and this draws on vComputer, so yes.