When you install Windows 2003 server, you will, as you probably know, lose the ability to boot into Linux temporarily (because Windows will always overwrite the MBR when installing).
So the first thing you need is a way to boot into Linux when this has happened. You can use a boot floppy made with the RedHat tools, or use RedHat CD 1 to boot the RH partition and then edit the GRUB configuration file to include Win 2003 Server and reinstall GRUB to the MBR, or if you have a LiveCD distro handy, such as Knoppix, Mepis, MandrakeMove, or SLAX, you can boot into that environment, mount your RH partition, chroot into it, edit the GRUB configuration and reinstall GRUB that way.
What else do you need in terms of multi-booting? You can read a tutorial I wrote, if you like-- :: Shell-Shocked :: Tutorial: Multiple Linux Distros
-- but without knowing what your specific goals are, it's pretty much impossible to advise you further other than to tell you how to get all three OSes to actually appear on a boot menu and boot when selected from that menu.
As far as accessing your shared FAT32 partition, I would suggest that you look in the file /etc/fstab and see if it is listed. If it is, then you only need type mount <mount_point>
in a terminal to mount it. If the line in /etc/fstab does not
include the "users" option, then you will have to su to root before mounting the drive.
If the drive is not listed in /etc/fstab, then you will have to mount it yourself (and/or include it in /etc/fstab, which file must be edited as root). Read man mount.
Then create a mount point (the traditional location for the mount folders is within the /mnt
directory, but as you see from my tutorial, I prefer to mount shared data partitions in my $HOME$ directory, and this is certainly possible). If you use /mnt, you will have to create the mount point as root, as users don't have write permissions to that directory.
Once that's done, open a terminal, and use something along the lines of
mount -t vfat -O option1,option2,etc /dev/hd* /mount/point
to mount it. This most likely will need to be done as root, until after you've added the partition to /etc/fstab, if you used the "users" option.
Hope this begins to answer your questions, if not, please be more specific as to what you're stuck on. Multibooting is a very broad subject.