Can't remove Partition table{MBR} virus NYB

I am using XP Home SP1. I am fixing someone computer.They had many other viruses which were removed. I ran an anti spyware and ad ware removal. They found many problems and removed them.The avg anti virus found this virus[Partition table{MBR} virus NYB] and it can't remove it. How do I remove it?
I will search the internet in the meantime. I can't spend too much time on this.
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