Until now I used a windows laptop with xp and the files where shared with samba. So I thought that using an unixoid os would bring some advantages :-)[ ... ]
I think that I'll use hfs+ on the emac.
The freebsd server should act as mail and news-server and also as file server.
Do I have to put the data on a fat32-slice?
If I setup a nfs-mount on the freebsd server and copy data from OSX to it, is the data readable from Freebsd without the hfs port?
Yes, NFS lets you share files without worrying about whether the local filesystem is HFS+, UFS, or anything else. If you've already gotten Samba working, you could use that to share files instead of setting up NFS: both work fine, but Samba filesharing might work a little better since the Finder supports it a little more gracefully...