The choice is relatively easy, how much are you willing to spend and what are you willing to give up to go lighter.
There are essentially three types of notebooks - regular, ultralight and tablet models. "Regular" notebooks are just that, the typical notebooks you see in the store with a nice screen, DVD drive, regular size keyboard, etc. "Ultralight" notebooks are portables that shed DVD drives and extra ports (USB, modem, VGA, etc), employ small screens and keyboards,
and use small processors to keep size down and battery life long. Ultralights are a trade off on portability and usability and they can be quite expensive for the higher end models. Tablets can fit in the middle of a regular and ultralight but have the added feature of a pen or touch screen. Tablets tend to be underpowered (relatively) but have good portability. (OK there are four - gaming notebooks but they are heavy, battery life that functions like a UPS but very powerful computers).
Mini-notebooks are referred to as Netbooks. They do not function as regular PCs but rather as portable internet devices. I am not sure how they run AC, someone else would have to comment on that. I am not sure that a netbook would be the best option since they tend to have a small screen (or rather resolution) that can frustrate users. One problem with netbooks is that they only have XP home installed which makes using them in an domain network difficult. You would have to purchase an upgrade CD to windows pro to interface a windows domain network. There are netbooks with Vista Business but I can not imagine those products working well at all because of the underpowered processors of netbooks.
In terms of the best ultralight portable, the MacBook Air is the best in class relative to price and features. Of course you will have to either dual boot windows or run in VMWare or Parallels. I personally use an IBM thinkpad tablet x61. I find that the tablets are the best portable windows products because portability is the key to a tablet function. Most of the true ultralight portables are very expensive like the Lenovo x200 or Sony's ultralights. I find that by getting a tablet you can split the difference of a relatively cheap lightweight and good performing laptop. Also on the car and ferry rides you can easily switch to tablet mode which provides for ease of use in tight spots.
I would mention that the tablet functions are difficult to use in AC, AC is not designed to be a tablet application.
Of course you can just shop around at the store for laptops like Best Buy, etc. and see if a "regular" notebook will work.
Geoff
