Can i use ddr3 ram in a ddr2 machine hp 7800

Is this yours? -> HP - Compaq dc7800 Series Convertible Minitower Desktop/PC

Memory:
DDR2 PC2-8500, DDR2 PC2-6400, DDR2 PC2-5300
Memory Type: DDR2 PC2-8500, DDR2 PC2-6400, DDR2 PC2-5300, DDR2 (non-ECC)
Maximum Memory: 8GB
Slots: 4

In most cases, when u have DDR2, u cannot use DDR3, as it is different from DDR2.

Unless there is a slot for DDR3 too.
 
Take a look what is different.

On the bottom of the RAM stick, there is a notch in different place so users cannot place in the wrong RAM.

ddr3-ddr2-module-photo.jpg