Windows is re-installed by booting to floppy and running the setup program
off the CD.  Get a utility for creating a boot disk with CD support at
www.bootdisk.com and use it to create a floppy to boot the machine.  Note
carefully the drive letter assigned to the CD, eg R.  Then enter x:\SETUP
where x is the letter for the CD drive.

You may need to access BIOS setup to force the system to boot from floppy.
BIOS is accessed using a special key at system startup - the key to use
should be displayed on-screen while the memory count is ticking over. Find
the option that controls boot sequence and set it so that A is first.