As far as specs go, any laptop with a Core i3 or above (hell, even a Pentium dual core) and 4GB RAM will do the job, no need for a state-of-the-art graphics card because they only really make a difference with video and 3D stuff (as in gaming and rendering, not as in "stuff that flies out of the screen at you").
Your big problem is going to be the screen. Most laptop screens are ill suited for precision colour work, to say the least. I work on a regular Asus laptop and my pics look different on every display that I look at them, so I'm never really sure of what other people are going to see when I share them online. On the other hand, you can always purchase a calibration kit if you see you're starting to take things seriously...