How to upgrade the Xp service pack remotely?

Hi Guys,

I’ve got a list of computers with service pack 2 (Report generated by GFI LAN Guard). I need to upgrade the service pack level to 3 on those computers. What would be the best and efficient way to push the sp3 installation?

Please note: We don’t have Ms-SMS Server.

I’m trying with “PSTOOLS”

Regards
Umesh