Thanks for the help. This simple configuration works ok: After logging as ftp or anonymous, I can succesfully upload files to /var/ftp:
Thanks again for your help.
Edit: You must also make sure "ftp" owns the directory:
chown -R ftp.ftp /var/ftp/
If owned by root.root, you'll get this when trying to upload a file: "553 Could not create file"