Best thing to do is review a couple of the download sites listed at Mandrake main page. Find one that responds pretty well when you use your web-browser to establish an FTP connection to it.
For "Name", use something like the name of the site (this value isn't critical, it just can't be blank). Even something like "FTP Install Site CD1" is fine.
"Path" needs to be the full path to the RPMS directory (ftp://ftp.mirrorname.org/path/to/RPMS
"Relative" is generally something like ../base/hdlist1.cz
Repeat for each CD:
path to RPMS2, then path to RPMS3
and ../base/hdlist2.cz then ../base/hdlist3.cz
Hopefully that will work.
I'm sure you can do it with just one source listed, but I don't have any machines currently installed from FTP to view as a reference.