Hi Arfus!!
TBH, Marius would be better off giving you advice on this, but here's my 2 cents.
I assume you have no prior knowledge of orchestration, so you'll be basically starting afresh. I presume you're talking about Nathan Allen Pinard. He seems to use sound libraries like East West (EWQL) and Vienna Symphonic (VSL), and most probably with uses a DAW (Digital Audio Workstation).
So, in order to start off, you'll probably likewise need a DAW. There's lots of choice out there :) ...there's Logic, Cubase, Sonar at the higher commercial end of a few hundred bucks, there's the lower range DAWs like Fruityloops and REAPER at £50 each, to the freebies like Ardour and LMMS, which well, are free. However, I recommend you that you either buy a lower range DAW or try a free one first, as they'll probably be all you ever need, unless you're trying to break into the music industry.
Allem Pinard also uses several sample libraries. Again, there's lots of choice to be found. However, unlike DAWs, quality comes at a price. Here are some of the main ones...
EWQL (East West Quantom Leap) - this set of libraries are good, and at a more affordable price of $350 for the Gold edition. There are several versions, and others such as Silk, Symphonic Choirs, Ra, Stormdrum etc. so have a look around!!
VSL (Vienna Symphonic Library) - This is for more professional composers. Unlike EWQL, VSL is a lot harder to utilise, and less 'out of a box', but generally regarded as better in terms of sheer quality. This comes at from $500 to $18,000, so shop carefully :P
GPO (Garritan's Personal Orchestra) - Coming under $200, it's fairly good value for money. I used to not be a very big fan of it, but then I heard Knights and Magic by Richard Birdsall... wow
Freebies - and of course, for cheapos like me, there's free samples found on the internet. Although if manipulated carefully, they can produce high quality music, they cannot rival the other libraries in terms of sheer quality.