Where are they collecting? If in the Temp Items folder then chances are you are using system 9.0.whatever.
Apple changed its way of handling temp files -- temporarily. System 9.1 reestablished the old technique of sending them to the trash. If you do not wish to upgrade then there are freeware solutions that will do the housework fairly transparently such as Autopurge.
Did this solve your problem? If so, please consider supporting the PPT FAQ with a small PayPal donation.