To run a server offline, you don't need anything from your ISP. If you want to host your own website from your own computer, you need to talk to your ISP about that. They'll give you setup instructions or information to work from.
As for XAMPP and other installations, I find it best to just install it piece by piece (apache, php, mySQL) and then add what you need when you need it. I have found XAMPP to be not very forgiving in customization, so I stay away from it. If you google it, there are plenty of tutorials on setting up Apache, PHP and mySQL on a Windows or Linux box....