I’m thinking about upgrading my Nimbus 26" with a ISIS hub and KH cranks. I have average mechanical abilities. How hard is it to switch hubs, and should I put in new spokes with the hub?
Thanks,
Marty
When i went upgraded to my KH hub i got a biker mate to soke it 4 me he used the same spokes aswell but i didnt want to do it myself cos youve got to get all teh pattern of the spokes and not screw the rim up… thats about all the knowledge on changing hubs ive got 
Nimbus/KH hub dimensions:
Flange width-Center flange to center flange- 75mm, Flange diameter- 65.5 mm
UDC Cromo hub dimensions:
Center Flange to center flange distance is 71mm. Flange OD is 66mm.
looking at these numbers tell me that your spokes should be just a little bit longer with the KH or Nimbus hub but the difference is probably less than 1mm so you should be able to use the same spokes.
Sheldon Brown has an excellent tutorial on wheel building on his site.
I did the same thing with my Nimbus 24. I also replaced the new KH rim. Go for it, It’s not that hard to do. This book http://www.amazon.com/Art-Wheelbuilding-Reference-Neophytes-Wheelaholics/dp/0964983532/ref=sr_1_1/002-3699596-4174455?ie=UTF8&s=books&qid=1194111936&sr=1-1 The Art of Wheel building by Gerd Schraner is a great reference book to help you build it yourself.
You should probably replace the spokes also. They may bend at a different point coming out of hub and could weaken them. They are pretty reasonable price wise. Take your time and you’ll be very pleased with your first wheel.
Thanks for the input