If you are using grub boot loader, boot into RH and etdit the file "/boot/grub/grub.conf". You will see something like below:
default=0
timeout=10
splashimage=(hd0,0)/grub/splash.xpm.gz
title Red Hat Linux (2.4.20-20.9)
root (hd0,0)
kernel /vmlinuz-2.4.20-20.9 ro root=LABEL=/
initrd /initrd-2.4.20-20.9.img
title Red Hat Linux (2.4.20-18.9)
root (hd0,0)
kernel /vmlinuz-2.4.20-18.9 ro root=LABEL=/
initrd /initrd-2.4.20-18.9.img
The "timeout=10" that you system will boot the default settings after 10 seconds. Change this if you don't want to wait so long for a default boot. The "default=0" means it will boot the first "title ...". If your "title Windows..." the second one, then change "default=1"