If I am not mistaken Inspiron 5100 and 1100, use the same processor chip:
478 pin Northwood, but we cannot use the 3.06 that is Hyperthreading technology, but can use the one that has speedstep.
This is all new to me as well, but my CPU comes in the mail Wednesday and I will tell you if it works. Since I did not get any help as well.