The form factor for your motherboard is Micro-ATX. Are you looking to replace your motherboard, processor and ram? Depending on your needs for the computer and what processor and memory you currently have, it is pretty unlikely that you will see any substantial performance increases by going with the same LGA 775 chipset based boards.
Can you outline you needs, potential budget, programs used etc etc, that way I can give you a more precise rundown of parts, costs and process.