There's a GV app: Google Voice - Android app on AppBrain I have it installed on the NC, and I can use it just like it runs on my Droid. The only minor catch of course is that the App will think the NC is a phone, so when you install it, just link the NC to one of the numbers you have in your GV account (I think I selected my office number). It will also ask which calls (domestic, international, etc.) you want to make from the NC--for this I selected "never call." Probably doesn't matter.
Just did a few texts and they work great. The only catch is that contacts do not automatically populate in the To box. But I think there is a contact-hack for that: NookColor Making contacts work - nookDevs