like aramisathei said, for internet work and general use cpu doesnt matter too much. However i would look for a laptop/notebook with a minimum of 7200 rpm hard drive (if not a ssd). The lenovo g580 has a 5400 rpm hard drive.
What is, in reality, the difference in time of having a drive that is 5400 rpm as opposed to 7200 rpm or even ssd.
The G580 is marked down to 299 pounds and that seems a really good deal.
But as you say if the rpm is important I will look elsewhere.
Is there a simple web page that can tell me what I should look for?
The use of the laptop is..
Great deal. But for photoshop? A Celoron can barley process Windows itself, why would you use photoshop on it (try the original Celoron, I'm not even sure that thing had a processor in it)? So, I guess you could barley get away for basic internet use, for now, with that laptop. But I recommend looking into a custom PC for photoshop. Any laptop CPUs aren't the same as a desktop one. They use a lot less power (which the cost is low enough that doesn't matter at all, although it does if your running off a battery) but other then that they pretty much cut all the good things out like 3.0GHz+, lots of cache and just features I don't use but they just make my PC's specs look fancy. Same goes for laptop GPUs. Which I would like to mention that with the use of OpenCL with modern graphics cards you can do amazing photo editing without lag.
That all depends. Is it possible to spend more money? I recommend a laptop with an APU. The reason for that is because not just since APUs are cheap and are good for gaming due to the graphics but because of the graphics OpenCL would work well with it. With photoshop using OpenCL, it would be MUCH faster then a i7 laptop!