Comic book artists generally work on what looks like a 3'x1' page; once they have the layout right, it's reduced to the standard (8"x10" I THINK) size, colored, and text added. Most graphics programs allow you to create a page of the right dimensions and fit the images into it (though a publishing program would probably be better). I don't remember DPI settings (I've seen so many numbers tossed around that I lost track!). Do the images in whatever size you NEED them to be, then resize to fit the page is my suggestion. Either that, or follow the Time Extreme/ Pieces model and do one image per page, all with a uniform size. This seems to work best for online work, actually. Essentially, find out the size and medium you're going to publish to (web (any size), magazine (8.5x11), traditional comic (I THINK 8x10), mini-comic (4x5 or 3x5; I've seen both)) and then tinker until you have something that is both visually appealing and properly dynamic. There are some good books on the subject - Eisner's "Comics and Sequential Art," as well as "Understanding Comics" and its sequel by Scott something (I can't remember his name off hand).