First your gonna need a Image editing program like adobe photoshop 6, or paint shop pro 7 with animation shop three. You can download 30 trail versions of both of them from
www.download.com just type the name of image editing program you want in the search field.After that you you gonna need a hosting site like
http://www.0catch.com/ ,
http://www.angelfire.com/ or
http://www.boomspeed.com/ (
which is the best in my opinion)
Make your banners with the image editing programs you can find images from this site for almost any character
http://www.gamegen.com/ once you've finished you banner upload it to your hosting site and thats it. Easy as 1 2 3