OK, rather than using the somewhat flaky ftp capabilities within Safari (error when downloading), Chrome (no log-in script) and IE (refused access), I downloaded Filezilla and did it properly!
All 5 disks unzipped and about to be expanded to real floppies for my A600
Incidentally, if anyone fancies using Filezilla (or such a thing) the settings I used were:
Port: <left blank>
You'll actually end up in the main grandis.nu directory, so use your ftp client's explorer/navigator to open 'TheZone' and then 'Files' area.
Sorry if this is a bit obvious but I thought I'd post it for those having problems.
EDIT: The game plays great! Excellent work