QUOTE(Synesthesia @ Mar 30 2008, 04:25 PM)

I don't know about Photoshop and Paint Shop Pro, but if you open an image in Paint, you can choose to save it as a PNG from the dropdown below where it asks what you want to name the file.
it's the same thing in PS.
just go File>Save As & from the drop down menu where it reads "Format" select ".PNG" & there you go!