I have several northwood core
CPU's (all the mobile variants in desktop
mobo's). Speedfan and Hmonitor note that my
CPU is running at 69/70 deg C. This is so not true (bios says at highest 35 deg c). Basically I think it is my cheap
mobo which is not supported properly in either application. I am currently running a Northwood-256 (aka Celeron Mobile) 2.4g at 3.4g stable with a Zalman CNPS-7000B (what a heatsink). To sum up what I'm on about take a look at where you are getting these results.
(Speedfan did report the correct temps immediately after install but then screwed up)
If these are the case then check you have the heatsink installed correctly.
Pimps correct me if I am wrong. (I have an ASROCK p4vt8+)