You're doing it backwards. Copy the image into a new layer. Remove the background of that layer so only the part you want to be in focus is in focus. Blur the background layer...
Now you have what you want in focus in focus, and the background is blurred. You don't want to blur something and then unblur it, that's too much work. It would be something similar to this:
http://moffetimages.com/photoshop/cooper.htmlWhich yielded this photo:
Oh yes, this was with photoshop 3.1, so please don't tell me that there are easier ways to do this. There weren't with this old a version of photoshop
Brian