Can I get files off an iPhone 4 that is stuck in a firmware update loop?
Usually this is resolved by a second restore after you reboot your computer. Of course, you might wait things out if you don't have a backup and there is any chance whatsoever the phone will complete this update without risk of losing the data on the phone (contacts, app information, documents, etc...)

To be sure you (and I) haven't skipped a step, you will want to do everything on this page.


iTunes: Restoring iOS software


Pay attention to the link at the bottom should you get there about putting the device into recovery mode. That will wipe everything, so don't do that unless you have a good backup from this morning (or whenever you started the update process).