I dunno how to uninstall linux , I always have to go to windows and uninstall both windows and linux.
so how do I uninstall linux from linux itself?

You can't remove something while you are running it.

Simplest way: Remove the partition
Most secure: Wipe the disk

There are many tools for partitioning--one option is to get something like the Ultimate Boot Disk. All kinds of tools for partitioning, booting, etc.

If you are installing a different Linux distro, the installer will handle partitioning for you.

Either boot a live cd or boot windows, run fdisk and delete your linux partitions, then create a nice big new windows partition to fill with viruses

Boot in to windows, go in to disk management and wipe out your linux install. Make sure to remove all partitions and format.
Now you'll have to fix your MBR, so you can boot in to windows again.
Boot from your XP cd and go in to recovery mode.
Now either use fixmbr or fixboot or both what ever gets it done.
http://www.microsoft.com/resources/d....mspx?mfr=true
http://www.microsoft.com/resources/d....mspx?mfr=true
Reboot and windows should start.

*Note if you an error
I have done it a couple of times and it has always worked. However you see many having trouble with writing a new MBR, where neither of the above commands seem to work. The only explanation I can come up with is that you didn't wipe out your linux install completely. I done that before and had to use fdisk, because I didn't do it properly the first time.
Maybe someone has an easier way? And maybe theres a better reason why to fixmbr or fixboot sometimes fail to work, at least the first time around.