$12,000!!! for one computer? dang, you could build a network with that kinda dough..heck, you can get a decent laptop for $1,200..;)
Main thing is to get the fastest processor and most memory, first. The graphics card really doesn't count, get a decent one, but the turbo-charged models aren't going to speed up the render.
2nd thing, is that laptops go obsolete in less than a year (I came up with a time unit called the 'Comdec'..which is the interval between 1 trade show and the next..;) most laptops are made 'obsolete' in less than 6 months.
the Alienware PC's are a good bet, if you're into serious bucks.
3rd- if you're going the network route, you'll only have 1, 2 machines on it(I guess), so your network traffic isn't going to be all that much. 10mpbs cards will work fine, if you have that kinda cash to sport around, you can go 100mbps, if you'd like. Most servers are either dedicated to a few tasks, or are used for storage. Considering what you can get (100g+ drives for under a couple hundred), this shouldn't be an issue.
long story short, you could get all the droolware you want for less than half the amount you're talking about. It's probabaly the Scotsman in me, but I think you can get a real deal for a lot less.

I wish I'd said that.. The Staircase Wit

anahl nathrak uth vas betude doth yel dyenvey..;)