SAMBA, give me a break. There is no way I'm going to load the Microsoft SMB protocol onto my UNIX or Linux boxes. Make the Windows junk work like a UNIX box and load NFS onto it.
Free NFS client for Windows. I don't know of any that were ever worth a flip. I've tried Hummingbirds product, the old FTP Software product, and Intergraph's product. Out of those, I liked the Intergraph product the best (it had the best integration and least problems).
As far as using NFS for backups, I'm like everybody else on this board; don't do it. NFS is great for what it was designed to do and backing up directories wasn't its calling. Others on this board have listed great ideas. I would suggesting following those ideas.