Hi GMLear,
I've asked Greg to respond since I am not doing much development these days. I know MS changed things a bit in 2007. You should search for "regform.exe" which worked for IP2003 forms. For 2007, they changed MSI creation to be via Visual Studio and it was a bear to get working but I believe there was a solution. Anyway, you can make your form URN based and send it around as a restricted solution but then it can't publish to a SharePoint site. A restricted XSN does not need to be "installed". Just send them an XSN link in e-mail. Mel's blog shows how to create a URN based solution.
For a domain trust or full-trust installable MSI, please wait for more word from Greg.
Thanks!