What version of AOL are you using? If you upgrade from WinMe using AOL 7, it does break the connection because AOL uses a proprietary network driver not compatible with Windows XP.
Later versions of AOL still use the proprietarty network driver, but it is compatible.
The easy solution is to upgrade to AOL versions higher than 7.0--but, if that is not the issue, it would not surprise me if something else was broken by the upgrade.
Define DIRECT LINE...dial up? Or a broadband connection? Configuring a PORT doesn't make much sense....maybe configuring the connection's firewall....
Do you have anymore info on WHAT port needs to be configured? Any particular buzzwards they gave you (and why didn't they tell you what ports)
Seems odd...like AOL was pushing you off and blaming someone else. If this is really a problem, they ought to know what/how to fix it, it would seem. Millions of users have done as you and not had issues.
Provide more info adnd maybe we can work through it