When I installed Norton Antivirus 2007 My Computer(Windows XP) Works Very Slowly tell me or Suggest Me please?

I Purchased Norton Antivirus 2007 & when i installed it into my XP so it works very slowly & poorly Pickup performance when i start my pc.
Now tell me anyone what i will do to increase my pcs performance
Or any kind of software which help me
Or Some tricks to improve performance
Please tell me
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