Citrix MetaFrame Presentation server issue

Hi, I have facing a problem while trying to install Citrix MetaFrame presentation server for windows on a machine where Windows Server 2003 is running,
Installer Information
Citrix MetaFrame Presentation server for Windows can only be installed on Windows 2000 Server or Windows Server 2003 with terminal Service running in application server mode. Setup will now exit.
Need help from any expert ones to get rid of this problem
