Sarah,
will need
Photoshop or, ideally, Illustrator to accomplish what you want.
Though Davey will probably tell you that PagePlus can do it, though I doubt
that very much.
Actually, it does do it. From the help file:
To fit existing text to an existing line or shape:
1 Create an artistic text object.
2 Create a freehand, straight, or curved line (see Drawing and editing
lines) or a shape (see Drawing and editing shapes).
3 Select both objects and choose Fit Text to Curve from the Tools menu.
The text now flows along the specified path.
It actually is a decent and pretty powerful program for its cost.
Mike