This should help:
http://support.microsoft.com/default...BLN%5D;Q313348

How to perform a clean install of Windows XP

You would need a bootdisk to do this...you can boot from your XP CD and then during setup you will get the options for formatting.

Are you trying to keep the current install of XP? If so then you won't be able to do anything with the partition using fdisk without losing data. You can resize the partition and then create a new partition with the free space but you would need some program capable of resizing partitions like Partition Magic.

If you are simply trying to setup a fresh install of Windows XP then boot from the Windows XP CD and during setup you will get the option to delete the existing partition(s). Once you have deleted the existing partition the next step is to format...you should be able to make the partition whatever size you want...if you want to have a data drive or something then during setup just format however much space you want for the OS and finish the install and then once you get into Windows you'll be able to format the rest of the free space and it will show up as another drive that you can use to store your data in case you want to reinstall OS again you won't lose all your data since it will be on a different partition on the same drive. You'll probably want to choose NTFS as the filesystem...good luck.

Use Partition Magic to delete or reformat the partition

You can either use the XP CD to format the drive or use a WIN98 boot disk

You can only use a Win98 boot disk if your partition is FAT32 because Win98 doesn't recognise NTFS.

That didn't work for me because of the NTFS I presume .
BuddyB

I have windows xp home and my pc is very slow and it always giving not responding error

We need more info to help you out. Also, start a new thread for your queries.