The first thing you need to do is to fix your Master Boot Record (MBR). Using the Win98 CD or a boot floppy, reboot into Windows but only to the C: prompt. Once you're there, enter this command: fdisk /mbr
That will restore your MBR to a Windows-friendly state, allowing you to successfully bring up Windows. Next, you will need to reinstall the Linux bootloader. I recommend lilo, but Redhat uses GRUB by default. I'm not terribly familiar with GRUB, but the idea is that both options (Windows and Linux) need to be present in the bootloader in order for it to work successfully (obviously).
This issue is relatively common and I suggest searching here at LQ for more details or of course at Google. Good luck with it -- J.W.