If you're using PPT2002 or 2003, you can accomplish the continuous motion
using Custom Animation effects.

Add a motion path effect to the text box, either up or down depending on the
position of your text. You can move the text box off the slide area before
adding the motion path. Then, double-click on the motion path effect in the
Custom Animation Task Pane to open the Effect Options. Check the box for
"Auto- reverse".  Click the Timing tab and select Repeat Until Next Click or
Until End of Slide.

The text box will continuously animate up and down on the slide.

Julie Terberg
MS PPT MVP

PowerPoint Live: Sept. 17-20, 2006  www.pptlive.com

Hi Jeff

Tohlz gave this excellent response to a similar request:
In PowerPoint 2002/XP and 2003,
Click View > Master > Slide Master.
Create a textbox on the slide master. Type the text in the textbox that you
want it to run. Drag the textbox out of the slide, to the left side of the
slide.
Now, click Slide Show > Custom Animation.
Click Add effect > Entrance > Fly In.
Set the start to "With Previous", the direction to "From Right" and speed to
"slow" (you can adjust this to your preference).
Double click on the fly in effect to bring up the effect options dialog box.
Click on timing tab.
Click on the repeat dropdown field, and select "Until End of Slide".
Ok your way out.

If you have any more questions, post back :-)

Lucy