.tar files are files that have been combined to form one large file.
Have you verified they aren't viral with one or more anti-virus scans? There are free online scans available here:http://www.closedsocket.com/links.html
If you are worried about them, disabling system restore (even disabling it, rebooting, then reenabling it) will clean up the files in the restore directory.
Due to the fact that the tar extension is mostly unix based (which means that Windows didn't create them), you should be safe in deleting them, but more info on the attack question would better help us to give a definite answer.