CMOS checksum error message during boot after hardware changes

I'm trying to help a friend with a Dimension 8100 whose 80GB hard drive died after multiple power outages and restores during a period of several hrs while the computer was left on and unattended. The other hardware consists of a zip drive ,a CDR-RW, and DVD player. The system has a 1.5 GB processor and 512 MB ram, and was bought around 2001.
The owner bought 2 200GB Maxtor drives and said he wanted to use those and drop the zip drive. I first disconnected the power cord from the wall,removed the dead HD and disconnected the zip drive and then on primary IDE installed 1 Maxtor at the end of the cable and the DVD in the middle, then on secondary IDE installed the CDR-RW at the end of the cable and the other Maxtor in the middle. I did replace the original IDE cables with those that came with the new hard drives. All jumpers on all items were specifically set to cable select. I updated the bios to revision XP2 (apparently the latest?),booted into the bios to see that the new drives were recognized, exited bios and then got the checksum error message. I shut the machine down, disconnected power from the wall, removed the CMOS battery, and am writing this to ask for help before going any further. From reading a lot of knowledge base articles I do know to push and hold the power button for 10 seconds before reinstalling the CMOS battery, let alone doing anything else.
Please advise what to do in what order to resolve the checksum error message issue in terms of checking/adjusting bios settings (specifics PLEASE--I'm not familiar with the Dell bios). Please also advise any other actions that might be needed to diagnose/resolve this matter. I'm a brand new member and this is my first post--any and all help will be greatly appreciated!