256mb probably won't cut it once you start using sounds, which are going to come either from modules or samples. I think at 256, you may expect to be able to record a couple or a few tracks of audio, and as many midi tracks as you'll need. Maybe you can even process an effect or two.
As soon as you start adding internal audio ( samples / modules from within the computer ), memory goes quickly. I can tell you that Image line recommends a minimum of 64 mb for FL studio, but it doesn't take all that long for me to strain this laptop ( which has 784 ), when I start adding a bunch of effects and use internal modules or samples.
BTW, the new version of Tracktion looks nice, and promises better midi editing. Good deal, because it's predecessor was an excellent program otherwise. I'm still happy with FL though, and I'll stick with it since I already have other apps that are getting little if any use at all these days, like Sonar and XG works for instance.
AJ
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AJ