the old way: install a second Vista, before OOBE enter the Audit Mode, install the Sp2, run sysprep and generalize the image. Now reboot into your first Windows and capture the second Windows into a new WIM. WinBeta made a complete guide for Sp1, for Sp2 it's the same. You can use the WAIK from Sp1 to this, because Sp2 doesn't need a new WAIK.