Hub/wheel fitting

[sammo]

Hi,
I just picked up an '08 Specialized Hardrock, and I'd like to put together a set of road wheels/tires for it (I do a lot of road riding, but I want to have my trail wheels at the ready for the weekends).
I've got some experience with dirt bike parts, but I've never put bicycle wheels together before -- my main question: what specs/measurements do I need to know to make sure I get proper fitment? Namely on hubs... of course I'll talk to the guys at the bike shop next time I'm there, but I'd like to be able to do my own research first.
Thanks!

[Alex Ramon]

If you're building the wheels, you'll have to make several important calculations in order to figure out what spoke length you'll need. The only system I've used is the wheelsmith spoke length system, but it is quite a pricey investment.

There should be cheaper alternatives out there. Sheldon Brown has listed a few online spoke length calculators here: http://www.sheldonbrown.com/wheelbuild.html#length

Anyone know of some other good resources?