Sure, if you installed them both on the same system (meaning the same hardware configuration) then you will run into ALOT less headaches, but here goes:
Boot into RH as root.
I am assuming you are using lilo, if not, these are for lilo so you can either use lilo and do this, or wait for a response for a grub configuration...
open /etc/lilo.conf in your favorite text editor, for me it's
then scroll down to the bottom of the document.
There should be entries for RH already in there, if not, add something like:
image = /boot/vmlinuz
root = /dev/hdb1 (or wherever you have RH installed at)
label = RedHat
Ok, now that's just to be able to boot into RH, now below that add:
other = /dev/hda1
table = /dev/hda
label = Windows
and that will allow lilo to Windows as well.
At the top of the file, place a line:
default = RedHat
to by default have the better OS boot.
And then exit the editor and save the file.
And something like this:
Should appear if it was done correctly.