I just got a letus with a nikon-ai mount....is it possible to use older nikon NAI lenses with it. I can't seem to find any info on this.

personally i'd like to know the answer to this as well.
Im really not 100% sure what lenses work and which dont
for my newly bought Extreme.

Yes, you can use just about any Nikon lens with this mount.

May I ask, what are the differences in the lenses
Ai, Ais, Non Ai..etc

Go here for an explanation...too detailed to put in a post:
http://www.nikonlinks.com/unklbil/nomenclature.htm

This is a good link to describe and compare Nikon lenses but it does not help in knowing the BEST lenses for use with a cinema lens adapter. That is why when buying a lens don't take the risk on eBay of getting the wrong lens or a junker, but go to a specialist like lenses35.com who ONLY sell lenses tested and certified for the Letus. You pay a bit more because dealers have taken the eBay risk and hassle so you don't have to.
Indy

The answer is yes with reservations. Not all pre AI lenses are F-mount so be 100% sure before you buy.