There is no Virus in the Bios.
The CIH will try to erase the Bios but not place himself there.
Why do you think there is a Virus in it?
There is a simple boot sector protection built into the Bios (Bios Features -> VirusWarning) which will try to pop up a window, whenever any program tries to modify the boot sector, which is pretty normal, when installing any OS, so disable this option.
IMHO Leave it disabled, set boot order to "C: only" and install a decent Virus Scanner afterwards.
Latest Bios as well as other stuff is here:
http://th2chips.freeservers.com/ -> M537
(You'll have to wait two more days)
Bye
Thomas