The original post is several months old and he never posted if he fixed the system.
Perhaps if you could explain in more detail your situation, folks could assist.
The answers given will do the trick, if your whole hard drive was formatted to a linux partition(s).
If you know what make hard drive that you have, you can also use the manufacturer's utility to zero write or repartition the drive, so you can start over.
If you elected to have a dual boot system and now want to get rid of Linux and boot XP again, the solution may be different.
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"I love it when a plan comes together." - Hannibal Smith