You said you were messing with redhat. Can you still boot linux? I hope you can, cause a little bit of reading and then a bit of adventure with config files can save you lots of trouble. If you cannot still boot linux, consider reinstalling it.

once you have linux available on the machine booting into windows using lilo or grub only requires an adventurous spirit and a bit of research(assuming that all you have messed up is your MBR).

if using lilo, you can probably get info on setting it up to boot windows by following the instructions/links here http://www.tldp.org/HOWTO/mini/LILO.html

If you are using grub.. this might help you http://www.linuxgazette.com/issue64/kohli.html
or there should be lots of other resources available on the web about both boot loaders.