Convert InDesign CS5 file into a CS3 file

I have an InDesign document from my designer jn which I want to be able to edit the text (it's a service menu that changes occasionally). I only have Adobe CS3, and since the file was created in CS5, I can't work with it as-is. The designer sent me the files with the following message: "These were created in InDesign CS5 and unfortunately in InDesign you can only export an .imdl file that can be opened in CS4. Once it is opened in CS4, though, you can then export it as an .inx file that can be opened in CS3." She was able to export the .imdl file, but that was as far as she could go. At minimum I need someone to open it in in CS4 and export it as a .inx file for me. I would prefer to just have it sent back to me as an InDesign CS3 file. I'm uploading the entire original document package as well as the .inx file.