Finally CRM 4.0 has been released to manufacturing (RTM) and trial versions can be downloaded here: http://www.microsoft.com/downloads/details.aspx?FamilyID=a9c110fd-aac8-4d2a-b401-7801b1866e82&DisplayLang=en
I would also like to point out that there are (at least) three different media types in general released from Microsoft.
MSDN - Can use MSDN or Trial keys.
Normal - Can use Trial or "Normal" license keys.
Volume Licence - Can only use volume license keys. If you want a trial, use it for a maximum of 90 days and uninstall it.
This is important when installing a trial environment that might be upgraded to production environment in the future at a customer. Consideration has to be taken to their current license agreement with Microsoft, and you can never use the MSDN media to install a production server.
There might be exceptions to this rule, for instance, a MSDN media might accept a normal license key, but I would not expect it.
Microsoft Dynamics CRM Consultant