Sorry calv - I crashed out on you. Determining spoke length is pretty easy, as most manufacturers list the numbers for their rims and hubs. If you ever do need to measure yourself, this will help.

Also, another really easy spoke calculator can be found here.

There are also a couple of books you should look into and keep on hand for reference. The Bicycle Wheel by Jobst Brandt is a must have and The Art of Wheelbuilding by Gerd Schraner shows an extremely easy way to lace spokes that I find to be much quicker and more effective than the traditional method.