I can't comment on position, but I made two changes that greatly benefited me in terms of reducing/eliminating wrist/arm pain:
1. Get an ergonomic keyboard: The best kind are from Microsoft. I'm not talking about their curved keyboard, but rather their split-ergonomic keyboards. The 4000 model is the wired keyboard and the 7000 model is the wireless keyboard. Either one will do. It took me a couple weeks to get used to typing on but once I got used to it my wrist pain went away. It only comes back when I use a laptop keyboard now (or a straight desktop keyboard for long periods of time).
2. Get a fingertip mouse: There are two kinds of mice: palm and fingertip. I am a big fan of palm mice, like the Logitech MX510 or MX1000, but I recently changed to a fingertip mouse (Logitech VX Revolution notebook mouse) and that has helped quite a bit. Rather than resting your entire hand in what feels like an ergonomic position on a palm mouse, a fingertip mouse just uses your fingertips for movement and clicking. I don't know why the palm mouse wouldn't be better, but the fingertip mouse has reduced my wrist pain. The Razer mice are also good (I had a Copperhead that was really nice but wanted wireless).
I also got a couple giant mousepads to cover my desk with. It creates a softer surface for my entire workspace. I use two Ripper XXL pads from Xtrac:
http://www.xtracpads.com/produ...hp?prod_id=5§ion=1
I work on computers from sun up to sun down and ergonomics have proved very important for me in terms of being able to work the whole day without getting fatigued. I also recommend getting a quality LCD monitor. I had eye strain problems with my old CRT. I then upgraded to a 19" 4:3 analog LCD, but still had eye strain problems. After that I got a 20" widescreen with DVI which helped immensely. I currently use a 24" widescreen LCD over DVI - no more eye strain at all. I considered a 30", but aside from being hideously expensive, I had to turn my head to see the edges of the screen - not good for fighting fatigue. So a 20" or 24" LCD is a really good purchase if you work on computers a lot.
Chairs and posture also make a big difference, especially in terms of back, neck, and shoulder pain. I've found that soft, cushy chairs - while comfortable to sit in - are not good for using for long periods of time. I got an office task chair - a small amount of padding with a straight-up back - and it has been great for my back. Be sure to get out and exercise and walk around every few hours, even if it's only to get a drink or use the bathroom.