god thats an old thread!check this one out for a little inspiration Nano Tropica Aquacube 20x20x20cm [Now planted!] | UK Aquatic Plant Society they do look like nice little tanks mate good luck with it 🙂
In answer to the ops question then yes it is possible to grow those plants in there but you'd be better off with a filter attached. You really have to watch your water doesnt go icky too with the small volume in there so you have to keep on top of water changes. graeme edwards grew a stunning aquacube which will be on the archives here somewhere.