I went through nearly the same exact experience myself a few weeks back. I think many people who come here all have the same idea's and the same huddles to overcome, that's whats so great about this forum.
When I asked nearly this same question a few weeks ago, a user by the name "ocscully" pointed me to a website with a spoke calculator. Building Bicycle Wheels by Sheldon Brown
In my case the hub I was working with was not listed in any of the calculators which made it even more difficult.
My Hub/Wheel/Spokes post is located here
Guess I got lucky myself and the bike shop in my town has a very nice guy, who did that job for me and did not charge me allot. Some idea's, maybe the place you bought that hub from will tell you the spoke length? Your hub sounds like it will be more popular and currant then mine was, it maybe listed in one of those calculators, I also found out from my wheel builder guy, if the spokes are too long they just cut them off and thread the end with a tool, it takes a few seconds to do, but with 36 spokes, they would prefer not to.