PMView Pro (available for Windows & OS/2) has the ability to run conversion scripts for mass unatended conversion between a huge number of formats.
Besides that, [link|http://www.pmview.com/|PMView] is the best, easiest, fastest and most flexible image viewer-manipulator I've ever seen and worth far more than the $40 it costs. If folks had PMView there just wouldn't be dark and difficult to see pictures like from the NJ party. Slide up the brightness, slide gamma down to restore color intensity - takes a couple seconds. Cropping, color balance, rotation, all just as easy. Save in any format you like, with full GIF, PNG and JPG options.
Caviat: saves .eps (encapsulated postscript) but can't read it due to unacceptable licensing terms.