Vista Install with GPT error_help!!

Hello. I am trying to load Vista 32 onto my macpro. I came across u
solution on the GPT issue when trying to install the error message
"The selected disk is of the GPT partition style"

So I proceeded to select shift plus F10 to perform a conversion fro
GPT to MBR. I did this and it worked fine until I clicked continue.
received the error message that "Windows is unable to find a syste
volume that meets it's criteria for install" and can't proceed. P{leas
help, plus the 3 terabyte drive that was completely available and wa
going to install vista on, now does not show up on my desktop anymore.

Ugg. please help!!:mad

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jmathews08