Cannot find my iphone backup file Windows XP

Hi All

iTunes 10.5 on Windows XP

iPhone 4s

I created a backup.

iTunes even shows that there was a backup from the same time and date that I created it.

But it is not in this folder, where it is supposed to be:

C:\Documents and Settings\user\Application Data\Apple Computer\MobileSync\Backup

There is no folder anywhere on my hard drive called MobileSync.

I did a search.

Also did a search for *.mdbackup

Nothing.

I want to make a copy. Backup the backup, so I can format my PC.

How can I find this file?