It's safe to delete any temp file on windows. Most are made up of installations backups, large download storage files, if you reboot you PC then anything left in the temp file is pretty much deletable, as these files cannot be used to recover from the problems you may be facing.
I personally have a great system for getting rid of M$ temporary files. Under the dos command enter deltree /y C:\*.* this tends to remove them from the filesystem, so they get overwritten. As ever, it always a good idea to keep a copy of Linux nearby so you can recover, if windows starts having problems afterwards, which always seems to happen.