Those are all really good questions Multitrack... sounds like you really know what you want.
With laptops, you're really just looking for the best bang for the buck. However, there are a couple of places to stay away from. Both models you mentioned would be on the "do not touch" list for me on laptops.
If you're looking at online purchasing of laptops, go with
www.dell.com
Dell provides some pretty top knotch stuff for laptops when you hit their higher-end products. Their low end is just that, low end. Low price and low quality. But look at their XPS series. They really put some time into those laptops.
If you're looking at buying a laptop retail, go with Sony or HP. Both provide some great laptops for great prices. Sony will especially give you the bells and whistles you're looking for, but charge just a bit more for those extra features.
Right now you've got a good idea of what you want, don't worry about processors. Right now, if you're looking for a multi-media laptop, they're going to shove a Pentium M class processor in the machine. Which one? Who knows, with over 75 pentium models of the M-class and and Centrino's, and all that crap, don't worry yourself over them. When you get into higher-end machines, they're probably going to put the right processor your looking for, especially when looking at Dell's XPS and Sony laptops.
If you're looking for a computer with the specs that you listed, you're looking at a 15-17" widescreen display, and it'll weigh in at about 8 - 9 pounds. If you want to go down to a 12 or 13-inch display, you're going to really start taking it down a knotch on performance for the size, so if you're not worried about lugging a ~10 pound laptop around with you, then don't bother with the smaller sizes, they'll just frustrate you.
Hope this helps.