Well, it wouldn't be for the MBR. Not sure, but I wonder if the restore disks are making a recovery partion. (I don't think Dell does that though.) If that were the case however, it would likely have it's own drive letter already, instead of being labeled as "unallocated".
As far as the BIOS password goes, try this:
http://www.dewassoc.com/support/bios/bios_password.htmI know how big a pain it is, but if you are willing to reinstall again, there is an open source program you could use to wipe your "C" drive of all it's partitions and start fresh. It's a freeware Linux based app called DBAN. (Darik's Boot and Nuke) It's safe, spyware/virus free, and will clear out the entire drive including areas that Windows format doesn't touch. I deal with a lot of second hand computer parts, and I always use it to clear out old data on used hard drives before I use them.
http://www.dban.org/about