As mentioned by Matt, AB-Aqualine makes an elegant piano wire ceiling hanging setup for all their Aqualights that is just great--very easy to move the light up or down, or to remove it for bulb changes (costs around $30). If you're going to hang your light, I highly recommend it. I hung a friend's
3' Aquaspacelight by myself in less than 10 minutes, honestly...
If you don't really want to hang it from the ceiling, since you have an acrylic tank, another WONDERFUL solution is to go down to your local plastic/plexi mart/store (most major cities have one that will do almost any custom work) and see what options they might have for some sort of custom leg apparatus for your fixture so that you can stand it right on top of your tank; they stock round and square rods of all diameters, as well as plexi (or lucite) of any thickness that can be cut and joined in any size and configuration you specify. I have done this a couple of times and was shocked at the many options--particularily if you or one of the sales folks is creative minded (it's best to take your light fixture with you to the store for such custom work, also, rather than measurements, believe me...!)
They can usually configure most anything you can come up with. As an example for a doctor friend's waiting room, I once had them make a little 10" tall U shaped "bridge" out of clear plexi that was only a little larger than the 70 Watt halide light hood it would hold up. The center of the top of this U shape(where the fixture's lens would rest) was one large cut out. The acrylic bridge just sat on top of the tank, holding up the light fixture; because it was made of clear acrylic, and had the same bends on its sides as the TruVu tank did , it matched perfectly and looked just dynamite on this little 20 gallon planted tank. It cost $39 but was worth every dime, as patients passing through her office often commented on the "custom" tank.
I have also used 1/2" clear acrylic rod to hang light fixtures over aquaria–looks infinetly more elegant and stylish (and invisable!) than any sort of chain! To accomplish this, I simply drilled the ends of the rods to pry/attach stainless split key rings to all the ends. The split key rings can then be directly attached to ceiling hooks as well as the light fixture hood (you sometimes need an extra seperate split ring attached to the fixture). Total cost for two three foot rods is around $12 if I remember right, plus $2 to cut it... I had also invested in a special drill bit (also bought from the acrylic mart) for acrylic that was around $8... It made the drilling of the rod a breeze with a hand drill over an old piece of wood.
Hope this helps,
Todd