For most people, setting up their web presence is a key element of business today. Your web presence generally consists of two items - your e-mail system and your web site.
E-mail is generally included with your website hosting package in the form of a standard POP3 host for your domain. This will provide you with basic mail services.
If you are looking for calendaring and / or other features, you will need to look into something like Microsoft Exchange. MS Exchange can be purchased as a stand alone server, bundled in the Small Business Server platform, or you might opt to utilize Exchange hosted services.
Web hosting generally comes in two flavors: Unix or Windows. The kind of web site and underlying services will generally dictate one or the other hosting environment. If you don't have any special requirements such as databases, PHP, etc., then it will generally be your webmasters preference that dictates the hosting environment.