Thanks everyone for all your suggestions.
I think I am probably going to look for a nice core 2 duo laptop, something around 15" screen for portability reasons, with a native resolution of 1280x800 so that all my VIs fit in one screen nicely (no scrolling if possible!). Also, a dual output so that I can connect a 19 or 21" LCD for when I am at home.
Now I just need to find this for under £600!!
Thanks again.
Neil