Vista x64 Boot Camp in Parallels - Boot Camp Driver Installer Says Model Unsupported

I have several Mac Pros in my office that are Model 1,1. On two of these machines so far, I have tried to install the boot camp drivers on a fresh Vista 64-bit Business installation from the newest Mac Pro disc (a 10.5.2) (which I am hoping have the newer 64-bit drivers on the disc). In each case, I have gotten a message saying that x64 boot camp is not supported on the model Mac Pro that I am using.

My question is, is it possible to update my Vista SP1 installation to SP2 and have it work in both boot camp and Parallels? I ask because I also have a few machines running Windows XP SP2, and before I updated to SP3, I needed to update the boot camp drivers, to which I cannot do for Vista SP1 because of the message.

Comments and suggestions are welcome and appreciated.

- Kristian