If you get a seperate linksys router (like a wrt54g), it can handle the PPPoE interface instead of having to do it through Windows XP.
The disconnects could be related to a numerous amount of issues. If you are having packet loss, your dsl could be dropping all the time that could be causing you always to re login with PPPoE.
A good way to test, try a unlimited ping to a popular site.
Go to run, type cmd, get to a prompt then type
ping -t www.yahoo.com . Let that run for 20-30 times. If it does randomly drop off (no ping reply) copy that and email that to earthlink (if they will accept that email). You could at least copy/paste it in the chat.
If you get a Linksys router you can have it handle the PPPoE and it will take care of constantly relogging in your DSL. You will still need to use your dsl router (so you'll be running 2 routers).
Either 2 main possibilites. Your DSL is dropping packets so the connection is hanging up, or something screwy on their side or your windows box is making you have to constantly relogin by PPPoE.
Give more info to see if the status improves.