please help me i want to delete my computer window 7 and put windows xp

Not a good idea because XP is no longer supported. No more security patches will be released.

In any case...
Boot from the windows XP DVD. You can wipe out the existing partition during the setup process.

Hi, is called a downgrade , and MS does grant licensees downgrade rights under certain Windows licensing conditions
here are the details although as usual maybe a bit vague

http://www.microsoft.com/oem/en/licensing/sblicensing/pages/downgrade_rights.aspx#fbid=cp9fVT3S15G

This information also includes conditions relating to system builders.
I presume you are a private computer owner
Bluntly speaking you require a boxed retail-sourced Fully Packaged Product ( standalone) XP Windows Professional
You can downgrade with full support (in the downgrade licensing context) if the host computer has oem Windows 7 Ultimate or Professional
If you do not try to bootleg the licenses your computer should run XP without issues with MS
But as JorgeM noted XP Windows is no longer supported.
This is regarding development so will become increasingly prone to security compromise and possible instability regarding latest release devices and support software such as apps and drivers
Also generally has inferior graphics performance and self healing

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