Hi intrigue8995 and welcome to the Captivate community!
Sorry, but Captivate files are not backwards-compatible.
If I remember correctly, you can copy/paste objects common to
both versions between projects, so you might be able to create a
version 2-only version.
For example, captions and images are in both Captivate 2 and
3, so you can copy these from a version 3 project and paste them
into a version 2 project. However, rollover slidelets are only
available in version 3 so they cannot be pasted into a version 2
project.
Obviously, you need to own both versions of the software (v3
to copy the objects and v2 to paste into) and you'd also have to
maintain the projects separately going forward.
Not great, but assuming I'm not completely wrong on this, it
may work for your needs.