The readhat install should take care of it for you. BUT BACK UP EVERYTHING IN SIGHT FIRST. Make sure you defrag the windows installation first to make sure there is enough contiguous. free space at the end of the Windows partition to create the new linux partitions.
To be sure, you may want to use a tool like parititon magic to shrink the windows paritition down first of all. Linux has some good partition management tools but partition magic is probably the most feature rich.
On installation, what you want to achieve is keep the windows partition intact - though shrunk to make room for linux. Linux will want 2 partitions as a minimum - one for the file system and one for the swapspace (linux uses a dedicated partition rather than a swap file as in the MS world.
You can let the install do it automatically (choose delete all existing linux partitions and not delete ALL existing partitons on the setup). Alternatively, don't let the setup so it automatically and set it up yourself. Remember, as you are intalling on the same disk, the windows partitin needs shrinking first. (personally, I would rather recommend a second harddisk for linux).
The only other issue you may come up against with sharing one disk between to OSes is the 1034 cylinder problem. This only effects old BIOSes that could not real past the 1024th disk cylinder to load the kernel so may be an issue on an old system with a large disk. Once booted, linux handles disk access rather than the BIOS so once the kernel is loaded, all is fine. So to get around this, you'll need to create a small partition to hold the kernel and place it towards the beginning of the disk - called the /boot partition, holding the /boot directory which contains the kernel. Again, make sure the MS windows partition does not start beyond the 1024 cylinder so the best layout would be something like:
boot | windows | linux | swap
The best way to set this up would be to use partitino magic to prepare and relocate partitions prior to installing linux . Again, if you use seperate disks, this 1024 thing isn't an issue.
As most BIOSes are now OK, I would suggest only worrying about the above is booting fails onc installtion is competed (make a rescue boot disk during install of course.
Finally, when it comes to installing the boot loader, whichever one you choose (which should automatically configure itself for both systems), make sure you install it in the Master Boot Record (MBR) of the primary disk. That way, the loader will be the first program loaded and will allow access to both systems. Don't install it on the first boot sector of the root )/) partition as the MBR will still contain the windows loader and it will never get to access the linux partitions.
There is good documentation in the support section of the redhat website so check the for install details.
Norwich