There are plenty of examples for fileUpload functionality. The Richfaces LiveDemo site has one (if you download the source code for RF, you will see the backing bean code as well).
There are several s:fileUpload examples in the Seam distro as well.
Now which one to choose: s:fileUpload or rich:fileUpload?
The RF guys have put their backing bean source for the demo on line.
Don't have the URL here with me will post later.
Try searching the RF forums for it.
Once I looked at that then it was a breeze to get it to almost work ;)