This can be done pretty easily, without any special coding.
Assuming you have a default ribbon loading up with the database, and you want a specialized ribbon for a certain form or report:
Make sure your ribbons are stored in the 'USysRibbons' table, and you validate them, either by loading them one by one to verify they work, or by downloading and testing them with the Office 2007 Custom UI Editor tool, available at
http://openxmldeveloper.org/articles...mUIeditor.aspx.
In design view, go to Form Properties > Other > Ribbon Name
Select the ribbon you want as that form's default.
Now, this ribbon will open in ADDITION to your default ribbon. If nothing happens, then the ribbon is either exactly the same as the default, or it's invalid. (only takes one bad space or lowercase letter to cause the ribbon to fail sometimes!)
If you want -only- that new ribbon to show, you'll need to set within the XML of the new ribbon the following:
<ribbon startFromScratch="true">
If you need to get more dynamic than this, I really suggest reading through the three-part walkthrough at MSDN. This covers all of office 2007, but has Access-only examples as well.
http://msdn2.microsoft.com/en-us/library/aa338202.aspx