I was able to get this to work. For the common fields you want to display, each form must have the same fields, with the same names, and located on the same level (won't work if one field is in a section and the other field is not). Then publish all of these fields. You will then be able to submit the form to either library or a different library that has the same setup (same fields, same names, same level).
If you are writing to a backend database (like Access or SQL Server), you can create "temp" fields that store the same information as the database field. The "temp" fields will be consistant on each form and these fields will be published. This way you can keep the same structure like I mentioned above (if you have two forms, with two different tables, but similar fields, SharePoint won't recognize the fields if you publish the database field. This is because the fields are named differently because the table names are different. A "temp" field would resolve the issue).
Chip