Is it possible to tell windows to clear the temp folder everytime i reboot/shutdown the pc?

Some temp files may be needed during the next boot, so it's not safe to do that before shutdown.

one workaround (implemented in the cleanmgr tool of winxp) is to delete temp files only when they have not been accessed since a few days.

to automate this, run "cleanmgr /sageset:55", check the options you need and click OK.

then, create a shortcut to "cleanmgr /sagerun:55" in your startup folder and the cleanup will run every time windows starts

if you're not using xp, you can google for other tools (CCleaner,...)