Yeah..good luck on Whitney! I did the same thing..signed up for a guided hike up Mt. Washington a couple years ago. Our group was led by a fantastic guy..the head guide there at Eastern Mountain Sports, Joe Lentini. He was fantastic...just like most professional guides I've met he doled out useful information and set a just right pace the whole day. We had a balmy day on the summit with light winds..
Trip report here:
http://www.mudspike.com/lionhead.htm
I took that knowledge to the Whitney Mountaineers Route the following year in March and promptly got my ass handed to me by the mountain..

Though similar in some ways..the scale and exposure on Whitney felt much larger for some reason.. The 3 guides I've met from SMI were all the coolest though..I'm sure you will have an awesome trip!
Good luck on Whitney!
Chris