Check out www.sheldonbrown.com for info on riding posture.

There are a lot of helpful things on that site.

Also, I was going through the same thing recently - shoulder, neck and elbow pain. I decided I wanted to get a better bike anyway, so I decided to go to a LBS that had a good fitter, get measured and let the fitter know the troubles I was having.

I found out that I actually had a long torso for my height and that my bike was too small. So, I got a new bike (Trek 1500 WSD, 47cm) and he initially set me up with a 100mm stem with not much rise. I felt a little better, but still wasn't comfortable, so I went back and he gave me a 90mm with a 17 degree rise stem. This set-up actually feels comfortable. So...you might want to double-check bike fit, stem length and stem height. My handlebars are higher than my seat and this is what is comfortable for me right now.

I also figured out that doing exercises and stretches for my upper back and shoulders have helped quite a bit. Sometimes those areas can be weak and we don't even know it. So, every day I stretch and do those exercises and with that and the new bike fit I find that I am getting less and less sore and stiff.

I'd be happy to share my stretches and exercises with anyone interested. I got them straight from my physical therapist.