How can I connect multiple users to a server simultaneously at the same time? I am using Windows Server 2003
If you mean connection through remote desktop: This depends on the licensing model you chose during the installation phase. If you have not changed the default settings, two users are allowed to connect remotely plus one user working on the console (which may also be remotely). But there are also other licensing models. This page of the Microsoft website may help you if you have questions to the licensing models.