TEMP FILES. There are 2 files containing temps. One is temporary internet files, the other is the temp files
which you are asking about. Temp files are created when certain programs are run or installed. (Windows is SUPPOSED to delete these files automatically but it often misses LOTS and these files, if left behind, can cause many problems with your computer.) Temp files should be deleted when the application using them closes, but many times they are not. Over time, the files build up, take up drive space and can affect your computers performance. These temp files are safe to delete.
However, they do not automatically show up on your computer. They are in a part of the hidden files and you must configure Windows Explorer in order to see them. Apparently you already know how to access them.
If some don't delete, don't worry about it. If the program associated with the files is running, they will not delete.
You can try deleting the next time you log on to your desktop before you open any other programs. If they still don't delete, and you want them gone, boot into safe mode and delete from there.
Clear your cache on a regular basis. Assess what you have installed on your computer-are there programs installed that get very little use? If so, decide if you can get along without them and uninstall them.
Have folders and files with lots of saved photos or documents? Consider backing them up to another source-cd, external hard drive, flash drive-and deleting them from your computer.
Defragment-if it's been a while since you've done this, or if you have never done it, the process will take a while. Let it run overnight or during a time when no one will be using the computer.
Also take a few minutes to read this: Slow Computer?, Use this troubleshooting checklist
which can be found here:http://www.bleepingcomputer.com/forums/t/44693/slow-computer/