acpi.sys cpu utilization

I have a 3GHz dual core with 8GB of ram on Vista 64 bit and the "system"
process, that normally should only be a couple of percent, is always around
47%, regardless of what I do to the system (one of the cores is always at
95-100%). Using process explorer it's showing that it is the acpi.sys
process and I'm unable to do anything to that thread. The actual start
address within process explorer is
"acpi.sys!DeRegisterOpRegionHandler+0x48cc". I have tried to disable all
power aspects of the pc from within the bios (full disable and change from
ACPI capable to standard mode), this causes Vista too not boot...trying to
change the PC type from within vista to a standard pc is not accepted by the
OS. Any thoughts? I'm dreading a re-install from scratch.