There does seem to be some confusion between MOBO and or case temps. Seems different manufacturers use these terms in different ways, and use different sensors/locations that are not consistant/universal.
My Soltek AMD board will read temps from a new, internal, built in, AMD Athlon XP probe (what they refer to as ABSII), and from the usual mobo socket probe (for older Athlon chips). They have another probe, on a lead, that can be placed anywhere you choose. I have that probe hanging aproximately in the middle of the case, off of the MOBO. For me this is my true internal case temp, which I strive to keep very close to the ambient temp of the room, through the use of properly arranged case fans.
My temps currently are:
Internal CPU temp: 60 degrees
External CPU temp: 42 (what most MOBO's use, and people report)
Internal case temp: 30
The difference of 12 degrees , at idle, between the case and CPU edge temp, shows that I am note using a fancy cpu cooler (HSF). More expensive (and usually louder) HSF's will narrow this considerably.
On the subject of case fans, usually the rear exhaust fans are more important that the fronts. I have one in front that blows in across the hard drive, and 2 rear exhausts. I also have a side panel blowhole fan (blowing in at my vid card) on a switch, that I turn on during heavy gaming sessions (my over clocked, 300/600, TI4200 can really heat things up and start to show artifacts).
If you have drilled/punched fan guards, that are part of your case's sheet metal, cutting these out completely (and using the standard wire bolt on guards if you feel you need a guard) can make a noticeable difference in air movement and temps. This will also lower noise levels.
On a final note, don't be afraid to use the cheaper sleeve bearing case fans (cpu fans should be ball bearing). In a multiple case fan set up they can be noticeably quieter.
