I would also recommend getting the The Guide To Midi Orchestration by Paul Gilreath.
I played on the sessions for "There will be Blood" and also on the BBC Radio Broadcast of Superhet Receiver, which is the work that the music is based on. It was a result of Jonny Greenwood being the composer in residence for the BBC Concert Orchestra and some workshops we did with Jonny developing some of those sounds.
I also use VSL and can tell you that you cannot reproduce the effect at the beginning of the film unless they record some very specific samples, and even then it would be difficult.
The effect is for every individual to choose a different note from some indicated note clusters and then slide in pretty much free time to the unison note with different sections going in different directions (some up and some down). Even if you had the correct glissando samples you would have to set up 34 different instances (10 1st violins, 8 2nds, 6 Violas, 6 Cellos and 4 Basses. The other interesting thing about the sound was that we all had to try and make the sound "break up" by pressing too hard on the string (can you really see VSL doing these samples!). This produced the particular sound that you hear and it took a lot of work between Jonny's idea and the players working out how to achieve it to produce what you hear in the film. Hope you find this interesting and how about using some glissando samples and having a go.
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