Echo Y|If Exist C:\Windows\Temp\*.* Del C:\Windows\Temp\*.* >Nul

If you don't have or use AUTOEXEC.BAT then simply create one. Make VERY sure the PATH matches your TEMP folder location and adjust if necessary. Now, every time you restart your machine, the TEMP folder will automatically be purged.

CAUTION: If you don't understand exactly what you're doing here, please don't try this tip, you may wind up deleting your \Windows folder - don't say we didn't warn you.