There are a few exporters for Blender i have some, may i ask which ones you downloaded?
I use version 2.59 so im not sure how different it is to other versions.
Firstly you must locate the Blender Foundation folder which you can search for in the search bar.
If you have files such as io_export_ogreDotScene (is a python file i have, make sure yours is for the correct version) it can be used to export to .scene or .txml which then can be converted.
1. Place that file into the folder Blender Foundation>>Blender>>2.59>>scripts>>addons dont place it into a folder.
2. Open Blender and go to File>>User Preferences then click the tab Add-Ons.
3. At the bottom of that window theres a button "Install Add-On..." click that. Go to where your Blender folder is and from there go into the addons folder and find that script.
4. Click the script (io_export_ogreDotScene.py) and click Install Add-On.... once again.
5. Im unsure if the script needs to be selected itself. On the Add-Ons tab click on the left hand side Import-Export. Then search through and you might find something saying "Import-Export: OGRE Exporter (.scene, .mesh, .skeleton) and RealXtend (.txml)" that needs to be selected so tick the box.
6. Once ticked click Save As Default then your done.
This information might be incorrect but its worth a go. The script you should be installing should be 253KB large.
For the AC3D if you dont want to buy it you can re-download the program over and over again, or you can search for full free versions on Google
