There's an folder called hsperfdata in my temporary files folder that I can't delete. How can I get rid of it?
The hsperfdata folder has been put there by Java and it isn't intended to be deleted (so why it gets put into the temporary folder is a bit of a mystery).
If you really want to get rid of it, try logging in as an administrator from Safe Mode and delete it from there. However, the next time you run an application that uses Java, it will probably reappear.