You should be able to remove the dial-up configuration from the Network panel in the Control Panel.
You will probably have to remove the Freeserve account from your email client (Tools--> Accounts --> Choose anything relating to Freeserve and click remove)
You may also have to undo any customisation that Freeserve may have in IE (if you use it) - that requires a registry edit or removing IE and downloading a fresh copy from the web - I don't think there is any way to clean up IE.
Having said all that XP should have an restore feature which allows you to go back to a known configuration - in your case pre-Freeserve though, since I do not run on XP, I am not sure if it goes down that level of undo.
Good luck
amofw