Well, thx guys I succed in mount the nfs in the way mr Dre showed me.
Now it's configured like this:
ruDream 1.08 in CF (256Mb) default image;
240Gb volume in nfs (@ jpm: always running...

)
/var on CF
The problem is: now that it does the automount, I'm not more able to record with ngrab ("device unavailable" or something like this). More, the swap file, originally mounted in the nfs partition, does't work anymore. I tried to make another one (expert menu/memory ../swap file on hd) but now on /hdd I've mounted the CF (without enough space), while the nfs is mounted in /mnt/nfs (and doesn't exist the option "swap file on nfs").
Any idea or another sleepless night?
xisco