Try to make use of disk management in XP and then merely reformat the separator that 2000 is on. It will then clear out the 2000 installation and will leave you with an empty, formatted partition.

Now, the problem is that I do not desire to lose my obtainable information on my Win XP by formatting it. Is there any way without formatting the whole computer??

You must be having 2 partitions, C: for Win2k most likely and D: for XP, or vice versa. Immediately go in and select the Win2k separator and then format which might be the easiest way for deleting it. There you will not format your XP installation, but it'll just delete the separator. However as per my knowledge, you'll may delete all your boot record that I imagine if Win2k is on your C: drive... never in fact try this out.

I think that he is having both the operating systems on one partition only.

Yes I too think that he is having both the operating system only on one partition, they will be having dissimilar WinRoot Dir names, so that you can install it both on the same partition, then just delete the Drive: WINNT folder, as well as then edit the boot.ini with the notepad, which you ought to see a line like this shown below

[code:1:996c5d0855]multi(0)disk(0)rdisk(0)partition(1)WINNT="Microsof t Windows 2000 Professional" /fastdetect[/code:1:996c5d0855]

now delete the line where it is saying WINNT="Microsoft Windows 2000 Professional" (the full line) that’s all, would be more favored for cleaning the Page file, but it is not a truly a big thing for doing it.