Image Retouching / Edtiting Workstation

Hi, i am a 1st time poster.. long time reader.. if that makes sense

i am looking into setting up a complete image retouching mac suite,

i currently own a very old powerbook g4 and a imac 20" but i am looking at shelling out for something that will give me an almost industry standard set up

what i really want to know is what is the best option to go for, i would love to have dual displays as screen area is important but mobility is also important.

i usually get my macs straight of the shelf and would also like to know what upgrades or specs i should go for.

also any must have accessories or imputs to get?

i will mainly be using a raw image editor and photoshop but i tend to kill ram by working on a few files at once.

please could any of you with the know please assist


much appreciated