mATX case type is mini ATX. these cases are smaller than standard mid-towers and therefore, they need smaller motherboards. most good motherboards available at the moment are designed for ATX cases, and are called ATX motherboards accordingly. if you want to upgrade while keeping the same case, you'll have to look for an mATX compatible motherboard. as for powersupply.. 120watt is horrible. get 500+w at the very least. motherboard processor, if you want to future proof yourself you could get an AM2 motherboard/processor, which are very reasonably priced. or if you're a performance enthusiast you could take the intel route and get an lga775 motherboard with the intel core 2 duo (conroe) processor. if you're just looking for a computer that will work i'd recommend a skt 939 processor/motherboard from AMD.