Configure XP Home as WSUS Client

Simply paste these values in notepad and save as "reg.reg" and double-click it to import the settings. Where it says http://yourwsus replace that url with the url of your WSUS.

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate]
"ElevateNonAdmins"=dword:00000001
"TargetGroup"=""
"TargetGroupEnabled"=dword:00000000
"WUServer"="http://yourWSUS"
"WUStatusServer"="http://yourWSUS"

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU]
"UseWUServer"=dword:00000000
"AUOptions"=dword:00000002
"AutoInstallMinorUpdates"=dword:00000000
"DetectionFrequency"=dword:00000001
"DetectionFrequencyEnabled"=dword:00000001
"NoAutoRebootWithLoggedOnUsers"=dword:00000001
"NoAutoUpdate"=dword:00000000
"RebootRelaunchTimeout"=dword:00000010
"RebootRelaunchTimeoutEnabled"=dword:00000001
"RebootWarningTimeout"=dword:00000015
"RebootWarningTimeoutEnabled"=dword:00000001
"RescheduleWaitTime"=dword:00000001
"RescheduleWaitTimeEnabled"=dword:00000001
"ScheduledInstallDay"=dword:00000000
"ScheduledInstallTime"=dword:00000000


One side affect of using these registry settings to controll Automatic Updates is that any ability to control setting for AU in the Control Panel will be disabled and if you try to change the settings it will fail with an error message. Not too important as long as you have the right settings.

After this registry has been loaded, simply stop then restart the update service by going to a command prompt and typing:

net stop wuauserv

net start wuauserv

wuauclt /resetauthorization /detectnow


source: Guide For Setting Up XP Home Clients With WSUS