what motherboard?
I'd guess MBM without knowing anythign else, because:
Windows readings can have a known "load" level. Bios Load levels vary from motherboard to motherboard. ANd no motherboard i've ever seen is either full load nor full idle in BIos, usually they're in hte middle.
I know a lot of people will disagree, but that's the truth... there are people who adjust windows "load" readings to match bios readings, but that's flat out wrong. Windows readinsg are exactly that, windows readings. Bios readings are only useful based on a load that hte bios puts the CPU under.
Mike