This is how you can delete/remove Linux from a dualboot system with Windows XP.

First take out your Windows XP bootable disc & boot your system from it. Then enter Recovery console by pressing R. In the recovery console prompt type the following commands:
FIXMBR
FIXBOOT

The GRUB will be overwritten & Windows will restore MBR & its bootloader. Just boot your system & windows will start automatically.

Now Right click on My Computer icon on your Desktop & click Manage. Click Disk Management.
Now remove all Linux partitions (These partitions don’t have any label & have unknown filesystem).
Now create new partition(s) in the free space. Format those partitions in FAT32/NTFS & now you can use them under Windows.

You can also try some awesome utilities like Partition Magic, Gparted to do the same.