If the files were never checked in they only exist on the user's computer hard drive.
If you can log in to the vault as the user then you can check the files in as if you are them. If not then your admin should help you get a copy of the files from the user's computer and undo the check out. You can then check out the files and copy the files from the user's computer and replace them.
Hi Ian, as Michael says, if the files were never checked in, they only exist in that user's local view.
If you can access that users computer, and log in to the vault view as Admin, then you can check the files in, and preserve the changes the user made locally.
Otherwise, you should be able to log into any vault view as Admin, and you will see the files as <Private> or <Local>, you can do a Undo Checkout, however since the files were NEVER checked in, I'm not sure of what the effect will be.