Silly question, but after reading "saved in the same folder on my desktop" I have to ask - are you testing this using IIS or some other web server software on your desktop?
If you're just opening the local HTML page directly (double-clicking on the file vs running a local IIS and going to http://localhost/
or however you have it set up), there's no server running the actual ASP/VBScript code.
Also, reguardless of the answer to the above question, you should definitely fix the <form>
tag as Guido Gautier mentions in his comment to your question.
This:
<form method="post" action="contactusaction.asp"/>
Should be this:
<form method="post" action="contactusaction.asp">