There are two basic ways to convert photos to a different format:
1- Use a software program which runs on your computer to convert the image.
2- Use a website service (many are available free) to convert the image.
SOFTWARE PROGRAMS
If you are using a Windows computer, the Gimp for Windows is an open source photo/image editor which can convert images into different formats. To import images into Windows PhotoStory3, convert them into JPG format.
On a Macintosh computer, the built-in "Preview" application can be used to convert images into different formats: JPG, PNG, PDF, etc.
Picasa is a free program from Google which can be used to do some image editing. It is available for both Macintosh and Windows computers, and can be used to save images into JPG format.(convert them.) This is a help page on saving Picassa images.
WEBSITES
Picnik is a free website that can be used for photo editing and conversion.
ZamZar is a free file conversion website, which can (among other things) convert images into different formats including JPG.
Not sure about the conversion. I'll check - but I know at photoshop.com/express, you can sign up and photoshop has an online photo-editing program that does lots of neat stuff, and it's FREE!