No problem.
FontSprite supports png files with a certain name format.
The format is as follows:
nameXxY_font.png
so a font with the name hello and a pixel size of 10 x 12 per character would be
hello10x12_font.png
There are a number of default fonts to play with in the fonts folder
Let me know how you get on, or any other questions you need help with :)