Preferably open source, but I'll take free (as in beer) if that's not available or even a commercial product if it is clearly the best option. I know there is a client built into Enterprise and Ultimate editions of Vista, but I'd rather not upgrade just for NFS.
Soren asks for alternatives/instructions in the comments:
The nekodrive on google code looks like it could be promising -- however it falls short on good instructions and it look like it is only available for 64bit, so I would accept an answer which would provide installation instructions only and/or for a port for how to install on 32bit.

