Hey guys, I've run into the same problem with the Winpoet and Mindspring DSL Software. But WinXP gives you a way around that.
Load up internet explorer, got to tools then options and click on the connections Tab. Set up a new connection as "Broadband Connection" while you are on the screen to set that up, at the bottom there will be a place for you to type in a Username, Pass and domain. Put your Mindspring/Earthlink info there and you should be able to dial up with no problems.
Rien