QUOTE(bobifier @ Jun 4 2009, 07:18 PM)

Having fairly recently passed my grade 8 piano, I felt that the world was my oyster and so, despite the warnings of the various pianists I know, took it upon myself to learn Rachmaninov's Prelude in G minor, opus 23 no. 5
Was I one of them? It isn't on the LRSM syllabus for no reason

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..., which, typical to his style, is simply a huge succession of huge chords.
Now now, that isn't entirely fair, Rachmaninov has
two styles - huge chords, and slushy film score. Though with regard to the latter, it isn't written as slushy film score, just often played as such

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...so I thought I should ask, how best to play and practise these chords? The way I play, I will most likely not be able to play it from start to finish without my arms giving out, so any help would be appreciated

Technique needs working up in stages, so it's a case of working out how best you can do that. In terms of how to attack a single piece with many instances of big chords, of which this is one, skim for difficulty with respect to this criterion and attack the passages in ascending order of difficulty. The answer which you likely won't be to pleased with is to learn at least one easier piece full of big chords first - the entry level for this piece is far above what would be ideal.
In terms of what you can do to help, the first bit would be to understand what's going on. Conceptually, you need finger tension for the split second the keys are going down to hold the shape and get all the notes to sound at the same time. Simply, once they're down, the down weight of the arm is sufficient. Wrist tension is comparatively less useful, but often builds up along with repeated bursts of finger tension. By way of example, clench your right hand and grasp it with your left; then, do a burst of squeeze-then-relax with your left hand. What will likely happen is a rapid burst of hand squeezing-then-relaxing, initiated by the fingers, accompanied by tension and slow release in the wrist. Further, if you then try do squeeze-release repeatedly, as fast as you can, you'll be able to feel the tension in your wrist build up. On the piano, this translates to a build-up of wrist tension with repeated finger twitches for rapidly repeated chords.
Tackling this - approach from two fronts: (i) build up finger strength, so they can hold their own with less wrist involvement; (ii) build up wrist pliability to help avoid the problem in the first place. For the former, dig out some exercises (e.g. Beringer). For the latter, assuming you've done the obvious (staccato passages in sixths and octaves, played with wrist staccato) then grab the metronome, start slowly, and build it up. Pick a passage that is under the fingers, and play again and again. No pain, no gain.