InstantDrummer Sessions do work with RiffWorks T4.
Here are the Installation Instructions:
Steps for Installing InstantDrummer Sessions
* Download the .swd file from the store, choosing Save in the download dialog.
* Make sure your browser didn't change the name of the file, for example changing .swd to .zip, or adding [1] to the name of the file.
* Double click the .swd file.
* A dialog will open saying the InstantDrummer sessions is installed and ready to use.
* You do not need to quit RiffWorks to install InstantDrummer sessions.
If it still doesn't work, please have your friend contact support with which operating system he is using, and which InstantDrummer sessions he purchased and is trying to load.
http://www.sonomawireworks.com/support_form.php