When talking about "how much RAM", it doesn't matter what kind of physical memory you actually have installed. Whether it's DDR or SDR doesn't matter when you're just talking size.
A 256 and a 128... My stinking laptop will only take up to 512 so I figured i'd just wait until the 256's are dirt cheap (or free) and just used a 128 my sister was chunkin. Damn I wanted at least 2G's. Why? I honestly don't really even know...