I have dual-boot with Win XP Pro and Redhat Linux(Fedra Core 3).
I have installed WIN XP Pro first (format with FAT32)
and then Fedra Core Core 3.
At partitioning stage, I choose "Automatic Partitioning", after then
I choose "a boot loader".

It boot finely either with WIN XP Pro or Fedra Core 3.
But the problem is when I boot into Fedra Core, I cannot see
the /dev/hda3 on my Fedra Core desktop? How to make it appear
and access?

/dev/hda1-WIN XP Pro
/dev/hda2- /Boot -> Fedra Core 3
/dev/hda3- / Where all FC files should be.

You'll need to use something like Knoppix mount the system and edit your /etc/fstab and add a line like;

/dev/hda3 / ext3 defaults,errors=remount-ro 0 1