I'm new to composing, sort of, and I plan on getting Sibelius 3 and maybe some extra sound libraries for writing music... but I'm going to be using a laptop, preferably a Notebook (I know i should compose on something better, but for convenience's sake and the priorities i have now, this will have to work for me for a bit).

I have no idea what I'm looking for computer-wise to support a composing program. I want the program to be able to run fairly decently so I'm not constantly wanting to beat my laptop with a sledgehammer, but nothing too unnecessary. What sort of stuff should i be looking for and what values I should be aiming for (for GHz and whatnot). Also, what sort of composing programs should I be looking at? I've heard great things about Sibelius, but I've also heard great stuff about Finale. Pros/cons for both?