OK Windows 2003 is an operating system (the latest windows server OS). IIS is the web server that comes with Windows Servers; IIS 6 being the latest edition of it. What you can do is lease, essentially rent, a server from an Internet company, where they can install this software, setup the database, as well as possible manage the server going forward. Then your users can connect to this remotely through of variety of means to use the software, such as a VPN for a encrypted communication or via the web server.
My company actually offers these services, dedicated server rentals, and if you want to go into this in depth you can send me a private message here:http://www.bleepingcomputer.com/forums/ind...sg&CODE=4&MID=3
From there I will give you my contact information so we can talk more about it.