CPU Upgrade on PE sc420

I'm looking to upgrade the processor on a PowerEdge sc420.  It has a Celeron D in it now (Model SL7TL) , and i was looking to go to a P4 HT chip.  I know that the bus speed can run at 800 and suports a p4, but my question is this.  What model 775 P4 can I use.  I assume that there is a limitation on what chips work based on the boards chipset.  Anyone have any ideas as to what model P4 chips this will support?  Is there a certain family of P4 I need to stay with?

 

Thanks for any info.