I had 80GB hard disk and in that both windows xp and Linux(RHEL-5) were installed.
I am facing some problem with windows xp and I decided to reinstall it.
After booting form windows xp cd I got the blank screen but I can able to boot perfectly from windows xp cd by deleting linux partitions. Can anyone please suggest me how to install windows xp without deleting linux partitions.

Simply install XP on a separate partition.

After booting from xp cd it gives blank screen then how can I select separate partition.

Your hard drive needs to HAVE more than one partition. If you only have one partition now, this could get dicey to reconfigure into 2 or more partitions without losing the existing data and having to completely reinstall both OS on the separate partitions.

You'll need a dual bootloader such as GAG or Grub

See:
GNU GRUB - GNU Project - Free Software Foundation (FSF) (http://www.gnu.org/software/grub)

GAG, the Graphical Boot Manager (http://gag.sourceforge.net)

You'll probably need www.sysyresccd.org (http://www.sysyresccd.org) to load it

And you'll have to modify boot.ini

Yep, he'll need to edit Grub or install and configure it.