I had RHEL 5 and WinXP on dual-boot and then from WinXP I deleted those partitions which were allocated to RHEL. Now I am not able to start my computer. The booting process stops at grub. I tried installing XP again so that it repairs the MBR for XP but the bootable CD is not initiating the installation process. How can I recover my winXP? Edit : I will not mind formatting the drive where XP is installed (in my case it's in C drive). Problem solved : Thank you guys for your help and support. I tried the RHEL cd and then in the command mode I tried fdisk -l and it showed that 1 partition was being used by Linux. I deleted that and then booted through WinXP CD and followed the steps which zypher suggested and it worked. 
How to uninstall RHEL from a dual-boot system?
linux;grub;dual boot;rhel
If you boot to your windows installation CD, you should see an option called repair console or something similar. Select that, it will bring up a dos prompt. Type the following commands: fixboot then fixmbr and reboot, you should be good after that unless there is something wrong with your windows install.