That depends on whether a computer case is considered to be a functional or nonfunctional item. If it's a functional item it can only be covered by a design patent or the equivalent design registration in the country concerned. If it's a nonfunctional item it is also covered by copyright,
according to wikipedia at least. The "AMIGA" Trademark in the A1200 case design is definitely a problem if you want to reproduce them though. Any US design patent is long since expired as they only used to last 14 years (new ones now last 15 years).