I agree with Alex. Ram is one of most important things when considering printing.
If you are going to network printers ( If machine offers it) then a good network card is also essential. A good calibrated monitor is also a good have. I personally like desktop monitors over laptop monitors as they seem to have more control over colors and brightness.
Other things to consider, these are not a must but they help. Processing Power (Quad core or better), solid state drives, video cards, operating systems.