This is a problem with the old version of compiz shipping in the Dapper repositories and with modual dialog boxes. This was fixed in compiz upstream a long time ago. Syncing compiz to the latest version will solve this bug.
FIXED RELEASED UPSTREAM -- Cannot move "Save As" box https://launchpad.net/bugs/35609 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
