Interesting Idea--EarthLink will roll out a beta of a new members-only Flash-based Web e-mail within four weeks, the Atlanta-based Internet service provider said Thursday, in a bid to upstage rivals such as America Online and even Google. Unlike other Web-based e-mail systems, such as America Online's new subscriber-only service, EarthLink's upcoming Enhanced Webmail is built using the Laszlo platform, which generates Flash- based applications. Most existing online mail services, including those hosted by AOL, Google, and Microsoft, are built on DHTML (Dynamic HTML