MS Paint

I actaully do it all in Ms Paint. 

1.  Save the file as a Bitmap in a place that is easy to find. 

2.  Locate the file on your hard drive and open it up (should default to the MS image viewer)

3.  one of the icons along the bottom allows you to open the image for editing (it looks like a painting with a paintbrush).  Click on it.

4.  It will open the picture in MS paint, just choose "save as" and you can choose the image type from there.

Off you go!  make sure to take a look at the post about uploading images to the site, it's stickied somewhere around here and is worth a read.

~rb