There is no direct way to make AOL Webmail the default email program because the operating system requires an application installed on teh computer to make it default (which is why the AOL Software worked for you in the past.

One option, if you are willing to test "beta" software and use another browser is the latest Beta version (v1.2) of the Flock brower at http://www.flock.com. It does a great job integrating AOL and other webmail products into the browser.