Well nothing comes up on a google search (strange if it is a google tool) for 3936_zip_dump.cab or 3936_zip_dump.dl_ or zip_dump.exe, which under normal circumstances I would say is suspicious.
What is the trojan name given by avast ?
What is the full path to the file/s ?
Some trojans deposit their contents in the temp folder/s so it may not be google's desktop search (I don't use it so I can't say for certain). However, if it were to do with the Google Desktop Search, other avast users would also be experiencing this and this is the first I've seen on the forums.
Download the program appropriate for your OS (?) and run it,
Ewido Security Suite If using winXP or
a-Squared free if using win98/ME, preferably from windows safe mode