I did one of these last month for my MIL's birthday... you can see a pic of the cake and close-up on my site:
http://www.patacake-parties.com/Birthday/Birthday.html (top row)
I pretty much did the same as cai0311... but I used black flowerpaste mixed with dark green sugarpaste to make the bottle.
I covered the bottle in clingfilm (Saran?) and then dusted with icing sugar before putting the paste over it and trimmed it half way. I left it to set for a few days, but once or twice, I just very gently released/lifted it from the bottle, just to make sure it would come off OK.
Here they are, still on the bottles for support, drying... you can see the greeny/black colour...
I got the sheen on the bottle by using confectioner's glaze, mixed with the tiniest bit of claret colouring, just to give it a slightly wine colour. I gave it several coats of glaze, letting each one dry before applying the next.
Make sure you do let the panels of the box dry before applying... you can see mine weren't set enough and are slightly bowing.
Hope this helps.