Soundslides itself doesn't have built-in title slide capabilities, so you'll need to create your own title slide as an image and import it into Soundslides.
An intro text slide can be created in most any image editing application. I typically make mine in Photoshop. Basically, I create a black image at the same size of my slide show (if you're not sure what size you're exporting to, use 1000px wide by 665 high).
Then I select the Text tool and add my title text to the center of the image. Then "Save as..." to a jpeg, and import into Soundslides just like any other image.
I've always used Photoshop, but there are a few folks on the forums here that swear PowerPoint is easier for making nice text images. Evidently, you can save the slide as a jpeg in PowerPoint as well.