There are other Microsoft only bios. This doesn't indicate that the entire bios is Windows only. It just means a tiny part of the bios code prevents installation of Linux. The easy way to install Linux on such a machine is to go into the bios setup program, remove the hard drive from the boot devices list, leaving only the CDRom as a valid boot device. And disable any executable bit security.
Boot from a live Linux CD.
Get Rid of Windows:
Launch a terminal emulator and do:
dd if=/dev/zero of=/dev/sda bs=4k count=10000
after dd, hit the up arrow, and repeat the command two or three times.
Then, reboot the machine with a Linux install CD, and install Linux.
If the above doesn't work, try this first:
Disconnect all power. Clear the bios with the bios clear jumper, or by removing the battery for 10 minutes.
On a different machine, make a DOS boot CD with a bios image file and flashing utility on it. Get the bios image file and flashing utility from the motherboard manufacturer's web site.
Remove the hard drive connections. Connect power. Boot with the DOS boot CD. Flash the bios. Reboot the machine with the new bios, hard drive still disconnected, and no CD in the drive. The machine won't boot.
Shut down and reconnect the hdd. Go into the bios setup program and remove the hard drive as a boot device. Continue as above.
Then, after you get rid of Windows, and Linux is installed, write Steve Ballmer a letter, telling him you destroyed your windows installation by writing Linux over it, and it made the machine work better.