PortFolio Magazine Technology ColumnWritten by Tom AnthonyMay 19, 1998 Pick up most any newspaper and odds are there is a story somewhere about doing business on the Internet. You would think that just about everybody is making money hand over fist on this global computer network ‑ but that’s not really true. Some companies are doing exceedingly well selling everything from books to mailing lists. However, most of the business on the web involves selling exposure, not products.  Some of that gold lies in the form of the banner ad, a rectangle of information usually about the width of a postage stamp and about three quarters as wide as your screen. …