Installing today the last version of Vbox, and updating also the GA...
I tryed to Move a File (Shift+Drag) from Host W7 to Guest XP.
The guest stuck, and I found the file in Temp folder.
C:\Documents and Settings\User\Local Settings\Temp\VirtualBox Dropped Files\
BTW, I don't understand why you need to use Temp folder of the Guest. The user should see and find his file where it is placed even if the Guest/Host crashes.