1. Install Winetricks.
2. When you open WineTricks you'll see a menu asking "what do you want to do?", you need to select the 'install an app' option. In the next screen select Adobe Digital Editions - 2011. Then just install Digital Editions as before; which is easier if you have your Adobe ID to hand.
3. Leave Digital Editions open. Then open Firefox and find and click a download link for an epub encumbered by Digital Editions.
4. In the download dialogue box select "Download with Digital Editions" and check the "Do this automatically..." option.
6. Open Calibre. Use the big + button in Calibre to import the e-book from your My Digital Editions folder to your Calibre library. After connecting your e-reader to your PC by USB you use the 'Send to device' button to copy the e-book to your e-reader. I know this is a bit of a bother, but it's necessary as it's impossible or difficult to get the wine version of Digital Editions to recognise the e-reader.
7. Optional: install cuttlefish and instruct it to open Calibre when you connect your e-reader to the PC via USB.
Hope this helps. Happy to suggest other options if you get stuck.