Users often have problems with drag & drop after clicking "Run Picard" from the Windows installer. This is because the installer runs with admin privileges and thus Picard will then run with admin privileges, which intentionally breaks drag & drop due to UAC.
Even worse, I've seen anecdotal reports that sometimes if the user then uses Picard to rename/move files, it can end up creating files with only admin privileges and the user does not have write access from their regular user account without taking ownership of the files and mucking around with Windows privileges. This is not something most users want to do
One option to address this appears to be using the NSIS UAC plugin from http://nsis.sourceforge.net/UAC_plug-in which the installer runs two processes; one with user-level privileges as a wrapper (and for launching), and another with privileged escalation.
Some investigation would be required to see if this is a worthy trade-off and whether it affects things negatively for Windows XP installation.