firstboot-1.4.30-2.fc7 Attached is a screenshot I took on my laptop. The native resolution is big (don't remember on top of my head ;), obviously larger than 800x600. Although I saw the full UI, the screenshot got clipped to 800x600.
Created attachment 148690 [details] screenshot-0000.png
Are there any tracebacks or other obvious error messages printed on tty1? Is there a /tmp/firstboot-crash.log file? Can you reproduce this by running firstboot --debug from a terminal inside X?