Either right before school (to take advantage of back-to-school deals) or sometime between Black Friday and Christmas are probably best.
As for stats... I need to know a few things. What Operating System do you prefer? Windows XP, Windows Vista, Mac OS X, a linux distro (probably not, because I doubt you would be asking for specs in this case), etc...?
Second, what do you plan to do with it? Only web browsing, typing papers, listening to music .mp3's and watching DVD movies? These are all extremely basic capacities which virtually every computer today will meet, so if you only want to do this, you should aim for the cheapest laptop possible. You should only care about more power if you plan to do something more taxing. For example, run modeling software (for architecture or civil engineering, etc...), heavy video editing, etc...