I've been successfully using XAMPP on Windows XP SP2 to run a local WordPress "Sandbox" since the 1.4.x series. I've recently upgraded from version 1.6.5 to 1.6.6a (full uninstall of 1.6.5 without removing the database or htdocs folder and then ran xampp-win32-1.6.6a-installer) and although everything appears to work fine as always I noticed that 1.6.6a, when starting MySQL and Apache, invokes a second "explorer.exe" process which continues running even after stopping both MySQL and Apache and exiting the XAMPP Control Panel. I have to use the Task Manager to kill the second "explorer.exe" process manually. The 2nd "explorer.exe" process usually is running at approximately half the memory of the actual OS's "explorer.exe.

I'm not that versed in the actual workings of XAMPP but isn't shutting down Apache and MySQL supposed to automatically kill the 2nd "explorer.exe" process?