ARod
Any users who you wish to be able to view your InfoPath document will need 2
things
1: The InfoPath client installed locally
2: Access to the original template (.xsn) file you created.

So if you are sending them the output from the form template (.xml) it will
attempt to communicate with the template relative to their machine hence if
you create a form on your local machine and store the template in
C:\MyTemplate\MyTemplate.xsn then fill out the template and send the
resulting MyData.xml  file to your user. When they open that file it will
look on their local machine for c:\MyTemplate\MyTemplate.xsn to render the
information.
I would suggest either publishing the form template to a shared location or
a SharePoint form library that you both have access to, you will then need to
recreate the file you originally sent from that newly published tempalte and
re-send it.

Hope this helps

Cheers
Ben