Updating a live install???

[WF8Sjake]

I am installing a live version of Fedora 15 onto a 80GB external usb drive for use in a college IT class.

Now I have tried this before but my problem is trying to run Software Update. When I use the graphical version it nver seems to finish as I let my attempt on Monday run for 24hours before I interrupted it. When I try to update thru YUM it get about half way thru installing the updates when the screen goes black, and the computer is non-functional until I restart it.

I have had this same updating problem using a 16GB thumb drive as well.

Is there something I am missing???

Thanks for any help you can give...