I don't believe you can change that information it is hard coded into the Ftpsvc2.dll file.
http://support.microsoft.com/search/preview.aspx?scid=kb;en-us;Q316998
You can configure a welcome message of course:
Start the Internet Service Manager (Start - Programs - Microsoft Internet Server)
Select the FTP service on the machine you wish to configure
From the properties menu select Service Properties
Click the Messages tab
Enter text in the "Welcome Message", field.
Click the Apply button then click OK
Stop and restart the FTP service
I know this isn't what you ideally want, but I don't think you can change the initial hard coded FTP Banner.