Seat post - how little can you get away with?

Any good links to cycling position and posture? My current position leaves me with a bar of tension across my shoulders, yet I was really careful getting the right frame size for my height

http://sheldonbrown.com/pain.html#shoulders
http://tinyurl.com/ydtmsvh

Google is your friend here.

Sounds like it's too small. what's the standover like?

Or too big, having to stretch too far/too much weight forwards.

Murray, just do lots of research with Google and mess around with different positions/setups. Failing that, go to a bike shop and get fitted. They'll sort you out.