Post the SSPEC, the five character code that defines the characteristics
of the processor. My bet is your P4 has FSB800 (i.e. it is a P4-C)
and something on your board is not rated for operation that fast.
If you want to look up the processor yourself, see:
http://processorfinder.intel.com
If it is an FSB800 processor, try using _only_ one stick of ram
and place it in slot 3. One stick of ram should be stable at
DDR400, assuming the one stick of ram is rated for PC3200
or higher. If you want to use more ram, put the second stick
in slot 1 and drop the CPU FSB clock manually in the BIOS so
it will run stable.
HTH,
Paul