Grub menu recovery after install Windows XP

Actually, there is an easy way to recover the problem. Just use your Ubuntu
Desktop/Live CD.

1. Boot the your machine with Live CD.

2. Open a terminal

(Application > Accessories > Terminal or type 'Alt-F2' and type 'xterm')

3. Start grub as root.

$sudo grub <enter>

4. Check your boot partition

grub> find /boot/grub/stage1 <Enter>

(hd0,3)

Note: Result (hd0,3) Harddisk 1, partition 3 (you may have more than 1 HD)

5. Fix your partition

grub > root (hd0,3) <Enter>

6. Setup grub at MBR

grub> setup (hd0,3) <Enter>

Checking if "/boot/grub/stage1" exists. yes

Checking if "/boot/grub/stage2" exists. yes

Checking if "/boot/grub/e2fs_stage1_5" exists. yes

Running "embed /boot/grub/e2fs_stage_5 (hd0)". 17 sectors are embedded

succeeded

Running "install /boot/grub/stage1 (hd0)

(hd0)1+17 p (hd0,3)/boot/grub/stage2

/boot/grub/menu.lst". succeded

Done

grub>

grub> quit <Enter>

7. Reboot and take out your CD live. If everything is fine, you will get
your Ubuntu bootloader again.

Happy trying...

Full Tutorial
https://help.ubuntu.com/community/RecoveringUbuntuAfterInstallingWindows