thought Id share in case someone else struggles with this as it took me ages to find the magic combo.
I have the original apple tv, I have a MyBookWorld NAS (network) drive (white light version) (MBW) I am running windows 7 on my pc.
first thing to do is to log into your web interface for your MBW, you can get to this from the configuration folder off the network drop down when you open my computer on your pc.
you want to go to advanced mode > network > services
check the NFS box to enable it, and add the ip address of your apple tv in the IP Allowed field (you can get this from the apple tv, google it if you cant find it - I cant remember)
go to your nitoTV and create a manual share point
enter the following
name: whatever you want
address: ip address of the MBW (get it from te url of the web interface or go to advanced > network > lan to get it
req auth: yes
login: MBW username - prob still admin
pass: MBW password you changed when you first logged in, if you didnt you can cchange it in the admin area of the MBW config
vol path: the default is /nfs/Public but the page where you enabled nfs with tell you at the bottom what this is if it doesnt work or you have changed it.
auto mout on or off if you want
leave the rest and save it then mount away!
Hope that helps someone out, it took me a while to figure it all out.