Is 51 DegC for a P4 650 3.4MHz cpu normal idle temperature?

First off I would recommend a new heatsink/fan for that cpu. The Intel supplied one is both too loud and inefficient. The thermal pad that is included on the bottom of the intel HS/F is way too thick and doesn't spread evenly. When I removed the HS/F to replace it I found that the thermal paste was almost gum like and had melted to one side. I replaced it with an Artic Freezer Pro 7 w/ Artic Silver 5 and my temps went down to 32C and it's much quieter with Asus Q-fan enabled in the bios. As far as temps changing with Asus Probe, the temps reported in Windows using Asus Probe(or any monitoring utility) will be few degrees lower than the temp reported by the Asus bios. If you go to the FAQ section on Asus's website, it explains that this is due to the low power states (C1, C2, C3) that the cpu enables when idle in Windows. The bios doesn't support these features so your temps will be a little higher in the bios.

Yes, i think those temps are abnormally high, considering that the ambient

temp is 16c and it's on an open bench... not even in a case. I would pull off

the HS/F and check to make sure that there is good contact. Clean up the

H/S, and at the very least apply some AS5.