Well, that all depends on whether you're using the LILO or GRUB bootloader. I'm betting that you're using GRUB since that is the default one for RedHat. What you'll need to do is edit the file
/etc/grub.conf and change the default to Windows. If you post the contents of that file here then perhaps I can help a little more... I'm a LILO person myself so I can't remember what the exact line is
