In reply to Sam longley:
Having been up the mast sorting out mangled kites in all sorts of weather, I usually just clip into my climbing harness and shimmy up the rigging in my Dubarry's then get winched up the rest.
However, when time allows I use a caver's harness and a croll and a jumar, with a mate taking in on a halyard as a safety back up line which is used to lower me back down.
The caving rig basically provides two "clamps". THe croll is linked at chest height and the jumar, looks like a large metal handle, goes above. You connect a long loop to the jumar, and put your feet in it. As you stand up the croll rides up the halyard, then locks when you put weight on it. You then take the weight off your feet (via the croll) and push the jumar up and repeat.
If you are feeling really brave both pieces of kit can be replaced by things called Petzl Tiblokes, but these can be iffy in extrmis and chew up the halyard after time.
To make life easier, a crew member can still take some weight on the safety halyard.
This is a bit extreme but gives you an iodea what goes where. A local caving club or climbing wall should be able to take you through the basics.