Everybody knows that you should regularly backup
your hard drive
(and you do it, riiiight?
Most folks have no idea what is in their CMOS, sometimes referred to (incorrectly) as their BIOS. For background, the BIOS is basically hard instructions, but when you configure your computer through the setup utility built into most PCs, you're putting those custom settings into CMOS RAM, which is either battery-backed or static RAM.
There are several freeware programs that can copy your CMOS settings, such as CMOS or CMOSRAM2, available over on shareware.com or downloads.com. If you'd prefer to do it the old-fashioned way, here's how to do it:
Make sure your parallel-port printer is on, and start your computer. When appropriate, go into the setup program (sometimes you need to HIT THE F1 KEY or another key to get in). Once you're in, starting with the first page, hit the PRINT SCREEN button on your keyboard. Windoze or any other operating system is not around to intercept the print screen request, so it gets dumped to the parallel port. Go through each page (sometimes they're nested or have tabs that you can scroll through). Take a "picture" of your settings and keep the pages with the documentation for your hardware. Should anything happen to your CMOS, you now have a snapshot of when it was correctly configured, and you can go back in and set the options as they were using your printed cheat sheets.
When you exit CMOS, make sure you select "Exit, do not save changes". If you accidently changed something, you don't want to have it impact your "good" settings.