Moving from a single to dual CPU setup

[Gerard Samuel]

I acquired a SuperMicro dual slot one board a while ago (http://
www.supermicro.com/PRODUCT/MotherBoards/840/PIIIDME.htm), 
and was running a single PIII 450 in there for about a month.
The system worked great.
I decided to move to using dual processors, so I acquired 2 PIII 667 cpus.
(According to Intel's site, they state it should work in a dual CPU setup).

Now in my mind, Im thinking the process of moving from a single setup to a 
dual setup is ->
1.  Make sure the system runs with one processor.
2.  Install second processor.
3.  Rebuild kernel for SMP operation

For some reason, when I install the second processor, and boot the box,
it hangs at random places during the boot process of FBSD.
If I boot the box (with the 2 cpus installed), and go to the bios screen, it 
will sit there, and not hang.
If I run FBSD with either one of the PIII 667s it will work great.
So my question.
Is there a particular sequence of events that must happen when going to a dual 
CPU setup??

If not, has anyone have any problems with the motherboard that Im using??

Currently using: 4.9-RELEASE-p1

Thanks for your advise..