you're definitely confused. you can't install DDR2 memory in the same slots as DDR. unless that is one of a few particular Pentium 4 motherboards that have both 184 pin and 240 pin slots you can't install them on the same board (even then not at the same time). as for SATA you will also have to check your motherboard has SATA ports. i suggest you get at least one 512mb stick of DDR400. having greater hdd storage does barely anything to increase performance.
edit: ignore the parts of my post where it seems i can't read properly. i just woke up and i didn't process all of your post