I'll assume that the 48" bulb is a normal output, 40w bulb. You can keep fish alive and happy with that, they don't really care. Live rock is fine, but more of the hitch-hikers are likely to die because they need more light. LS will also be fine. Basically you can setup a FOWLR but that's it. I don't think you can keep any corals, or anything that uses photosynthesis, for that matter.
Kris