ah vista through virtual pc 2004 unknown device

I have attempted to load WIndows Vista Beta 2 as a Virtual PC --
It gets to about 21% and then aborts stating unknown device---
Are their any known caveats and workarounds for installing to a virtual pc (actual machine 3.8 ghz Pentium with 1 gig memory.)
Any help would be most welcome -- thanks
-- Wendell A. Clark, BS
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