It sounds like a font issue is causing the input font not to appear.
Can you launch Font Book and double-check that Times, Verdana and Arial are all activated? Font Book is in your Applications folder. You'll also need to check that those fonts are not duplicated, as it appears that the duplicates are what typically causes a conflict.
We've heard of this missing input text issue from a few folks recently, mainly from people that have either recently upgraded their machine from 10.5 to 10.6 or have migrated a user folder to a new 10.6 machine.
If after checking the fonts you're still seeing the issue, try restarting into Safe Mode. Safe Mode will clear your font cache.
To start up into Safe Mode (to Safe Boot), do this:
1. Be sure the computer is shut down.
2. Press the power button.
3. Immediately after you hear the startup tone, hold the Shift key. The Shift key should be held as soon as possible after the startup tone but not before.
4. Release the Shift key when you see the gray Apple icon and the progress indicator (looks like a spinning gear).
After you start into Safe Mode, launch Soundslides Plus and see if the text input works correctly. Note: Safe Mode temporarily disables your audio, so we're only testing to see if the fonts are working properly.
Let me know how it goes.
Also, here's more info from Apple's site regarding Safe Mode if you're interested.