You might want to post that on the FC5 mailing list.
They might be able to help you better.
My guess is that something did no go right. From Googling the error message, I'd say that either mkinitrd did not got installed or run succedfully, or that there is a problem with the kernel you installed.
If I were you, I'd start troubleshooting by booting into rescue mode as explained here. Then I'd reinstall mkinitrd, the kernel and rerun mkinitrd.