Thanks very much for the replies. I appreciate it guys.
From what you've said, I'm tempted to just get a desktop PC now, as I'm concerned that a P4 laptop may have issues with overheating / noisy fans / breeze block appearance etc! Seems to defeat the object of portability and I'd be paying more than the equivalent desktop.
So...can I be cheeky and ask you to recommend a good off-the-shelf desktop PC for about £1300 that won't be too bulky but has the oomph I'm looking for and will be reliable? Ideally it would have Adobe Premiere included like the VAIO too

but of course that is a long shot I guess!
I'm not a techie unfortunately so I really need something simple that I won't have to fiddle around with too much (though I'd pretty much written off Apples as too pricey and not so good for non-editing duties?).
Any views you can give will be really appreciated.
Thanks again.
SebastianM