Sam points to NAnt 0.84 Final being released. Along with that, I found that the latest NAntContrib Project has been released as well. For tips on getting started with NAnt, check out a previous post where I describe my own experiences with the pre-release of NAnt 0.84.
Update: One follow-up to that post is that I found you do have point to explicit drive/file locations for GAC'd assemblies -- NAnt (really, its csc.exe that NAnt is using, so this applies to the limitations of csc instead of NAnt) is unable to reference assemblies stored in the GAC directly (unless they are also stored, as some System assemblies are, in the \WINDOWS\Microsoft.NET\Framework\v1.0.3705 area).
