if you boot using the floppy disk then the kernel image is loaded from the floppy, either create a floppy with the new kernel
/sbin/mkbootdisk --device=/dev/fd0 2.4.20-27.9
Or fix the bootloader, there's at least 2 ways you can do this but I suggest installing grub into the MBR. I'll assume your winxp is on /dev/hda, redhat on /dev/hdb, and bios is set to boot from C:, which is /dev/hda.
First backup your current MBR in case something bad happens
dd if=/dev/hda of=mbr.old bs=512 count=1
Then install grub into the MBR:
Lastly add this to your /boot/grub/grub.conf
If that didnt work please give more details on your disk configuration, 'cus I assumed a few things.