.QBB = Quickbooks backup file
.QBB = QuickBooks for Windows
.QBW = QuickBooks for Windows spreadsheet
.QBW = Quickbooks working file
.QDT = QuickBooks data file
You'll probably want to put all of these in, just in case your friend has differing types of files saved.
I would try starting a search on the root of the system volume. Also try looking in C:\Windows\Prefetch for any other Quickbooks related info. You might find files in here which lead you to places in your system that you never knew existed that the files are stored.
As another option, try asking your friend if he knows where he/she put the saved stuff.
Hope that helps
Jonathan 8)
PS.
http://www.icdatamaster.com/q.htmlPPS. If you want any more info, feel free to ask. All I ask is a bit more deatil for what you want to know lol