Why won't it work? Connect 3rd party POP & SMTP with outlook XP.

I have Earthlink as my ISP. I also have a online business
with a separate hosting company which offers their
version of email. I want to use or configure my company's
emails with my Outlook XP on my computer rather than
logging through my vendor's email application.

Questions.
1. Does an ISP have anything to do with my situation?
someone told me that SBC or PAcBell allows third party
connection.
2. Know where I can get the latest information on how to
configure Outlook XP with third party email applications.

I want to use OUTLOOK as my ONE source to check my emails.
If you can help, I would really appreciate your response.