I had a problem with my edgy installation. Firstly, I removed my problematic Dapper as well as its swap because of attempted to upgrade to latest version of program. Then, my Windows XP could not boot at all (Yes, They were from the same hard disk drive, different parition, hda1 is Win XP system drive with FAT32, hda2 is extended parition(NOT a drive),hda5 is FAT32 Personal Musics and Documents Drive, then hda3 is the Ubuntu Dapper system drive, lastly, hda4 as the Linux-swap drive accordingly in Gparted.)
Could not fixed Windows XP , I reformatted to whole drive except the personal drive. Next, I had reinstall Dapper through Live-CD, upgraded to Edgy Eft by Internet, which has no problem booting into Linux .Then, I later went to reinstall Windows XP with all its updates. However, now ,I could not boot into Linux anymore and Grub failed to showed (My PC uses NTbootloader to boot, I attempted to add in for Linux but failed). I made no backup at all before installing any OS (Be it Linux or Windows XP)! What should I do in order to make Grub showed so as to add in a line to boot both Linux and Windows on the Grub menu OR to modify the NTbootloader for the same aim, so as to dual-boot both OSes. I am generally fine with both options. (Note: My Dapper Live Cd is still working)
Thanks.

Try booting from the livecd. When it starts, you should have options: boot from livecd, boot from hard drive, and a few others.

Boot from hard drive. That will get you into Ubuntu from the hard drive instead of the livecd. You can then remove the cd from the cd drive.

Run 'grub-install hd0' (or possibly 'grub-install (hd0)' to write grub's first stage to the MBR of the hard drive. See the grub manual for the correct syntax.

Then su to root and edit /boot/grub/menu.lst to add an entry for winxp. Something like:
title Windows XP
root (hd0,0)
makeactive
chainloader +1

On re-boot, you should see entries for both windows and Linux. Try them both to make certain they work.