Does anyone know if it's possible to have 2 different Aras version installed (ie 11sp12 and 12.0) on the same machine for test purpose?
I assume il wil have separate databases and vaults.
This is most definitely possible. There are a few important things to note when installing your second instance. You'll have to ensure that the second instance has unique identifiers. This means it needs it's own file path, database name, conversion server path, and web alias. Each install will create a new database and each instance of innovator will have it's own vault. Going through the installation documentation in the 12 CD image should help you figure out how to set each one of these individually. It should be pretty straightforward, but let me know if you have any issues!
We want to test the version 12, so firstly in parallel to the 11SP12. We stopped installation since we had a doubt.
Installation is done in a dedicated directory, the conversion server path is also specific, based on dedicated web alias, but what about the "service agent" (the wizard is in French, so the translation could differ...)?
Defaut value is http://localhost/InnovatorServer/Server/InnovatorServer.aspx it sounds strange since this is the same for the both Innovator versions...