remove file from windows temp file

Hello,
My OS is Vista. I am trying to remove all files from my windows temp file. Most of the items in the temp folder I am able to remove by using select all then delete. The one I am not able to remove is called boot_interprosses it says it is a file folder. When I try to remove I get the error destination folder access denied. I have tried to use Unlock to try to unlock the file and then delete but that did not work. When I open the file skype_c2c_messaging_mutex appears. How do I delete this file and prevent it from returning? Please provide clear easy to understand instructions.
Also daily I get files/folders in the temp file that start with avg_ is there a way of preventing these from returning?

Thanks for any and all help.