Shsmith posted here!
In WM2003 the temp files always went to \TEMP. On WM5 most of these now go to \Application Data\Volatile, which is in your (slow) Flash ROM.
You can speed up a few things, as well as opening up more room by moving this folder to your SD/CF card.
Open a registry editor and navigate to HKEY_LOCAL_MACHINE\System\FileSys and edit the TempPath key.
I changed mine to \SD Card\Volatile. You may need to create the Volatile folder on your SD card (not sure–it may do it automatically).