Hi and Welcome !
Did you change boot priority of Hds before RHEL installation? Does GRUB menu appear at startup?
I would suggest you to re-install RHEL. Unplug Windows OS HD and plug-in other HD as Primary Master. Re-install Linux and plug-in Windows HD as Secondary/Slave after Linux Installation.
Boot up RHEL, log in as root and open /boot/grub/grub.conf file.
Add this code at the end of file :
Code:
title Windows XP
rootnoverify (hd1,0)
map (hd0) (hd1)
map (hd1) (hd0)
chainloader +1
Save file and reboot machine. Select Windows XP title in GRUB Menu.
Above method is safest way for setting up dual boot in Two HD setup. If anything goes wrong with one OS or HD, other OS will boot up fine.