Stu, thanks for the tip! Some of the stems were starting to grow horizontally when I took the plant out of its pot, and I've tried to encourage others to lay along the gravel or at an angle. I've started seeing roots on some of the stems, and when they're long enough I'll place them in the gravel. I figure it may take a little while, but eventually it should look really nice.
More about the cube, let's see...
It's a glass vase. I contemplated using a little plexi tank/container, but there's something about glass I find really appealing - it feels somehow warmer than plastic. I found a nice flower shop, went in and described what I was looking for, and they found it in a vase catalogue and special ordered it. I like the shape of the glass, the way it's bowed on the inside. It makes the cube more interesting to look at, but doesn't distort the view at all (after all, it's designed to show off the stems in flower arrangements). It wasn't cheap, but I'm very happy with it. The florist was really excited when he heard what I was going to do with it - maybe he'll have to start a pico of his own!
Osteomata, your tank sounds just like mine! This one was just set up a week ago. I can imagine it's going to be hard to keep it balanced, especially since neither of the plants I'm using are fast-growing. In my other tanks, the key to balance always seems to be loads of nutrient hogs - my 14g is mostly Crypts, and I'm constantly fighting off hair algae even though the NO3:PO4 ratio and CO2 are at similar levels.[/edit]