Which antivirus packages can be configured for on demand scanning only and will not load anything at startup? [closed]

"Easy, ClamWin. More free & open source suggestions from yours truly.

Straight off the site:

Please note that ClamWin Free
Antivirus does not include an
on-access real-time scanner. You need
to manually scan a file in order to
detect a virus or spyware.

also

Standalone virus scanner and
right-click menu integration to
Microsoft Windows Explorer; (context menu)

sounds like what you're looking for!"