the Xeons are a different form factor than Pentium4s, meaning a different number and location of pins on the bottom side of the CPU, and obviously sit in different sockets and thus different motherboards. Also they run on different chipsets.
in a nutshell - 0 compatibility.
One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them
In the land of Mordor, where the Shadows lie
M.C. Escher - Reptilien