DOS fdisk does not recognize Linux partitions. DO NOT attempt to just reformat the partition. First, we need to know a few things. If Lilo or Grub is installed, you need to remove it from the Master Boot Record first.
1. Do you have your Windows XP installation disk?
2. Do you have your RedHat installation disk?
3. Do you have access to PartitionMagic?
The article
here will explain a few things, but do not use the /fdisk /mbr command yet until we know what disks and software that you have.
Just to check, are you using Grub or Lilo as your lootloader?