915 based motherboards are generally LGA775.If you are buying a LGA775 based board and looking for a CPU for it,then these chips are available only in Prescott series.
Northwood core seized at Socket478.
ASUS does have a 915 mobo for the Socket478 . Any how its more logical to go in for the Prescott series due to the large cache and thus a better performance. Yes the Prescott series is not good for overclocking as the heat is a big problem. My advice go for the Prescott series.
I saw a rescue kit for prescott while reading some CPU reviews. One can google it to find it.
From what I saw, the kit looked like a First Aid Box. It had a USB fan to provide additional cooling for CPU and a Blank CD to backup important data, says prescott is not as immune to viruses as it should be.