Sadly, Parallels doesn't deliver the 64-bit environment promised by the Xeons.
Nor does VMware.
I find lots of MacBookPro stories, but not so much on the MacPro. Rumor has it lack of support for the SATA controller may be the blocker on the base ON SolarisExpress distribution, and I've been pointed at BeleniX as a possible solution...
Confirmation either way would be a grand thing.