DO NOT forget to make a backup copy of TPKX.VXD in your WindowsSystem directory prior to installing the P5-SR1 update.
The update overwrites this file and COULD cause both your P4 and P5 fail to startup and yam your PC. Should this be the case: simply restore the backuped TPKX.VXD, reboot your PC and both P4 and P5-SR1 should work fine.

You can find further info at Curious Labs`s twchnical support page.

Happy posing!
MaxxArcher