This effect is perhaps similar to the "God Ray" effect, which I haven't tried, but plan to. I suspect this is simpler, but doesn't offer as many possibilities as the God Ray thing.
Anyway. You add some text. With it selected, hit alt-c and make it into a curve. With it still selected, go into edit mode and add a bezier circle. Scale it large. This will create a circular "bezier sheet" with a text shaped hole in the middle.
Set your world horizon color to black. Make the above sheet black, tho I didn't in this blend file and it seemed to work okay.
Point your camera straight at the text. Put a spot light with the halo settings shown in the blend file behind the sheet, but to one side and then animate it moving across behind the text, put pointed toward the camera (see the file). The halo light shines through the hole in the bezier sheet and creates the effect. Sometimes you need more than one light..
You can play with the light distance and the clipping to control how long the rays are. The softness and blend also are interesting to play around with, as well as how wide the angle of the spot light is.
You can also use the same effect behind solid letters. Another possibility is to put the light in a fixed position and animate its energy level rather than its position.
This was made in 2.58, but the effect works pretty much the same in 2.49b.