I have a triple boot setup for FC3, FC2, and RH 9.0 on a computer with one hard drive. (I do NOT have a separate partition for the /boot directory.) You should be able to set up your dual boot in one of two ways, each of which involves editing /boot/grub/grub.conf. Print a copy of RH 9.0's /boot/grub/grub.conf file to use its information in subsequent configuration. First, you could install FC3 as the default operating system, and then (as root) edit FC3's /boot/grub/grub.conf by adding a menu choice such as the following to the end of that file:
title Red Hat Linux 9.0
kernel /boot/vmlinuz-2.4.20-31.9 ro root=LABEL=/ hdc=ide-scsi
Keep in mind that the current RH 9.0 kernel version and initrd that you are using MUST be used above in place of that given in the above example. Also note that (hd0,0) refers to the first hard drive - hd0, and the first partition - 0. If your Red Hat 9.0 is installed on a second drive, then you would have to reference that drive instead. Likewise, if your RH 9.0 is not on the first partition, then you would have to reference your partition instead. (See your printed copy of RH 9.0's grub.conf.) Also, if you have a /boot directory on a separate partition, your path may be different. (Type "info grub" at a terminal for further information, or consult your RH 9.0 documentation for grub.) As long as your FC3 installs smoothly, I can attest that this method works well. (Be sure to have a RH 9.0 boot floppy to get back into RH 9.0 if something goes wrong.)
Secondly, while I have not used this method, I believe that you could install FC3 such that its grub is placed on the first sector of its boot partition (rather than the mbr), leaving RH9.0's first stage grub in the Master Boot Record (mbr). (This should allow you to boot directly into RH 9.0 after installing FC3.) Print out FC3's /boot/grub/grub.conf for subsequent reference. You would then edit RH 9.0's /boot/grub/grub.conf, adding a menu choice such as the following to the end of the file:
title Fedora Core 3 (2.6.9-1.667)
kernel /boot/vmlinuz-2.6.9-1.667 ro root=LABEL=/12 rhgb
Again, you MUST replace what I have above with YOUR FC3 boot partition, kernel and initrd information as given in FC3's grub.conf file. E.g., if your FC3 boot partition is located on the third partition of your first hard drive, then reference <root (hd0,2)>.
Be sure to update your FC3 after installation. There is said to be a problem with the original udev that interferes with subsequent CDROM drive recognition. Also, you can make an emergency CD boot disk image for FC3 with the <mkbootdisk> command, following the instructions by Linus Rees at http://www.fedoraforum.org/forum/arc...hp/t-1272.html
There is a great deal of helpful information at http://fedoranews.org.
I hope this gets you on your way. I think FC3 is a fine distro, even though it takes a lot of post-install configuration.