Hi,
These are called Temp files, placed there by programs when you open a file, or modify it. Sometimes, they will be deleted in time, and some stay there until you delete them yourself.
Here is a link to a great, free, cleaner. This is better than the windows "Disk Cleaner" or whatever.
http://www.ccleaner.com
After downloading/installing it, you can clean out junk files (like the ones you have), Temp folders, etc, with just 2 clicks.
You can also go to Start/Programs, then open Windows Explorer. At the top, click on View, then Folder Options. Click on the Files tab, then left click on "Show all Files". Then, click on Apply and OK.
This will show all files to you, and they will not be hidden anymore.
You can manually delete them if you wish.