If you've got lots of pictures to convert, then a program with a batch conversion facility will be quicker than Marc's method. If IrfanView isn't already on your PC, it should be! It's a great picture viewing/editing program with loads of flexibility (including the ability to handle batch conversions). Best of all, it's free: http://www.irfanview.com/
just felt I had to back up Chris regarding Irfanview...it is the bees knees especially as it is FREE...and so versatile......screengrabs, you name it, a breeze to use too...commoner