If you go over 3gb or RAM you need an x64 OS to use the full amount. This can cause issues with some apps. If you don't have a reason for the extra RAM, get at least 2gb, but don't go insane.
You will definatly notice the difference between a 5400rpm and a 7200rpm during startup and when starting apps, but you won't get as large of drive for the cost.
Any graphics card with deticated memroy will perform better than an intgrated card.
I don't think that 802.11n cards are a good buy yet. Very few hotspots are n, and the ones that are are backwards compatible with G, and B. Even if you do get 802.11n you won't see much of a speed increase for internet use, since 802.11G is still faster than most internet connections. If you're doing large transfers on a LAN get gigibit hardwire, and plug in.
I prefer to have the largest battery I can get, so I don't have to deal with shuting down, switching batteries, ect. However, some machines are very awkward with the extended battery, if this is the case for the machine you're looking at then you may want to consider additional batteries.
Vista Ultimate some extra features, but you won't use them unless you're on a network with several other machines.
Personally I'm a fan of tablet PCs, I've got a
Gateway convertible that I'm very happy with.
If you're comfertible with it, you can save a significant amount by buying a chassis with the processor and graphics card you want, then upgading the RAM and HDD with parts from
Newegg. THIS MAY VOID YOUR WARRANTY.