How can I make windows XP as default OS & ubuntu as secondary?

Hello again, Dr Rai. My previous warning about editing grub settings still stands, but if you follow these steps it should be fine.

First open a terminal (Applications > Accessories > Terminal)
Now enter these commands:

cd /etc/grub.d

ls -l (That's LS -L in lower-case letters)
        (You should see a list of files: 00_header, 05_debian_theme, 10_linux, 20_memtest86+, 30_os-prober, 40_custom, and README; these confirm that you have GRUB2 installed. If they aren't there, STOP, check you've typed the first command correctly, then let me know and I'll change the instructions.)

sudo mv 30* 08_os-prober
        (At this point you'll be asked to enter your password)

ls -l
        (The list should be the same as before, except 30_os-prober is now 08_os-prober)

sudo update-grub

This makes grub look for non-Linux systems first, so Windows should now be listed above Ubuntu. Since grub ordinarily boots to the first OS on its list, XP should now be the default.

Hi Marc, thanks for your efforts.
But I did mention in my query that I ve grub 1.5 & not 2.
However thinking that you must be confirming the same seeing my expertise I did follow your instructions.
I got all the same list of files except 05_debian_theme
So does this mean anything?
Kindly let me know. Thanks

Yes, I wanted to check because, from 9.10 on, Ubuntu ordinarily installs with GRUB2 (though it appears as 1.97~beta4 at the top of the menu). I was overlooking the possibility that you might have upgraded from an older version of Ubuntu and retained the older GRUB version though. Sorry for that.

But the presence of those files (05_debian theme is for customising the background, so isn't really necessary) suggests that GRUB2 is installed.

In any case, my instructions won't cause harm. If GRUB2 is being used, then they'll work as expected. If the older GRUB is somehow being used, they won't do anything at all, and I'll tell you the old way of GRUB editing instead.