i've had good luck using this excel spreadsheet to calculate spoke lengths... use the tabs at the bottom to find your rim and hub dimensions, then plug the numbers into the first sheet, make sure you specify 3 cross lacing in the calculation.
Austin, Texas USA
> From: Matteo Brandi <email@example.com>
\r?\n> Subject: [CR] What spoke length?
\r?\n> To: firstname.lastname@example.org
\r?\n> Date: Thursday, February 26, 2009, 12:56 PM
\r?\n> im building a set of wheels for an on topic track bike.Im
\r?\n> using Phil wood hubs (white) with ambrosio balance rims.The
\r?\n> rims are "mildly" v deep.i would say
\r?\n> "AERO".Now,ive been suggested to lace them 3x
\r?\n> .Now,the guy that is helping me went nuts with spoke
\r?\n> lenght.What length for such wheel set?He say sthat he can
\r?\n> can get ACI or Dt spokes.
\r?\n> Thanx in advance
\r?\n> Matteo Brandi Firenze Italia