Operating system update from vista to xp

Question

I have ACER aspire 5720G with Windows VISTA. Just i installed XP without any problem. Now i have the following problems,

1. My notebook VGA driver is "NVIDIA GeForce 8400m GS Turbo Cache" and i could not find driver for xp.
2. I downloaded sound driver for xp, but when i instal, there was an error message as follows,
Realtek High Definition Audio
"Error (5006: 0x80070002) has occurred while running the setup"

3. When i open any window, can not smooth movement. even internet explorer.

Please advise me to solve those problem.

Farees
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