I heard of a virus a few years ago....
It apparently wrote to CMOS/BIOS and upped the harddrive speed or something to that effect. And the BIOS would then spin the HDD to fast, destroying your platters and such. I haven't been able find information on it anywhere....

Whether or not this existed, is it even possible? I know XP prohibits direct access to the harddisk, so you can't write to MBR (not yet anyways), but this was before XP. Theoretically, is it possible for a virus to modify the MBR on a FAT/FAT32 partition (Linux/Win9x), which would allow the virus to run a COM file before Windows loads, and then write to BIOS. I know different types of BIOS work differently, but you could just flash the BIOS anyways and replace it with garbage. Some newer boards don't even allow original firmware to be overwritten...when you flash, it writes elsewhere, to assure that you can't corrupt the BIOS. But most boards don't do that.