If you want to
obliterate the Red Hat installation, well, that's easy to do.

You just install right over it.
If on the other hand you want to
keep your existing installation, then what I would do, most certainly, is to
buy a second hard-disk drive. Most computers can select any installed hard-disk or CD-ROM as their boot-device. By choosing the appropriate drive you can easily install Linux alongside Windows, and not have to do anything special except select the startup drive right from the BIOS screen. (My machines even have a "profile" option that let me store entire settings and choose from them at will. All done in BIOS.)
When installing XP, I'd go one step further. After installing the new drive and verifying that you can see it from Linux, shut down the machine and gently
remove the power connector from the Linux drive. Reboot the machine, selecting the virgin new drive as the startup-device, and do a "normal" Windows installation from CD-ROM onto that drive. Because the Linux drive isn't even powered-on at this point, it cannot be seen and cannot be affected. It is "out of harm's way." You may need to be sure that the Linux drive is on "IDE chain #1" and the Windows drive on "chain #2" or somesuch. Fiddle around with it, carefully. As long as you carefully observe where things are cabled-up now (use a digital camera!), and work gently and be sure that all cables are firmly seated, you really can't
harm anything... once you get over the "under the hood for the first time" heebie-jeebies.
After finishing the installation, shut the machine completely down and gently reconnect the power to the Linux drive.
Now, you have options. You can add Windows to the GRUB boot-menu, specifying the drive upon which it resides, or you can do the operating-system selection entirely from the BIOS. (Note that you will
not have to fiddle with any power-cords on a routine basis.)
On my main "tinker with it" machine now, I have
three hard-drives and a DVD-ROM, all using the onboard IDE-controllers for simplicity. One drive is for user-files; the second is the primary system-residence (SYSRES) volume upon which the operating-system and Grub reside; and the third is purely a spare, also serving as an alternate SYSRES. Even if you no longer use an "older computer," don't forget that you can cabbage and continue to use its
drives!
For a laptop, don't overlook the usefulness of
external drives. I've got some very nice USB-2.0 drives (downward-compatible with USB-1.1 as all devices are), which fit in your shirt-pocket or a safety deposit box. They're every bit as fast as what's built-in. They draw power from the USB port itself. You can put stuff on there and boot from them. You can also boot a machine from a memory-stick or even a photo memory-card reader.
You are in no way limited to just one disk drive! Having more-than-one is of considerable benefit.