Yes, it does boot up before windows start.
Put a windows install CD in your CD drive and set your bios to boot from CDROM as first device.
Take a look at: http://users.bigpond.net.au/hermanzone/p1.htm#The_easiest_way_to_get_into_the_BIOS
, to get an idea how the settings wiil look in the bios. If you have another type of bios vendor, this will look different.
Search for the next text on that page:
Changing the boot sequence in CMOS
This setting controls the sequence in which the PC's BIOS will search for a bootable device at each boot-up.
The computer will try to boot the first bootable device it finds.
If you have a bootable floppy disc or a bootable CD-ROM, you need to set the BIOS to look in the floppy disc drive and/or the CD/DVD drive before it looks at the hard disk drive or your floppy disk or CD won't boot.