Cant get system to 0% idle

[Tuc at T-B-O-H.NET]

Hi,

	I have 2 systems, Dual Xenon's, both bought at the same time (1
serial number away from each other). At one time both ran 5.3, and both
could get 0% idle (Seti at Home, 4 processes). I've upgraded one to 5.5,
and now find ever since then I can't get the system below about 19% idle.
(I've even used benchmarks/ubench). 

	Short of the typical "Upgrade to 7" which I can't do (And for 
those jokers out there, can't go to 6 either).... Any ideas why this is
happening?

		Thanks, Tuc