Well, first, questions about FS2Open are best asked on hard-light.
Secondly, to install FS2Open, all you need to do is download the FS2Open exe and the Launcher, put them into your FS2 directory, and use them instead of the original versions.
To make use of the added graphical awesomeness of the mediavps, you need to download them from the release thread, put them all into a folder called "mediavps", put that folder into your FS2 directory, and then use the new Launchers "Mod" tab to select them as a mod.
To install Inferno, you need to put all the Inferno stuff into a newly created directory in your fs2 folder, then use the Launchers mod tab again.
As for your last question, while there is no "Open" version of FS1, there is a mod for FS2 called the FSPort, which ports all FS1 mission into FS2.
Again, questions like these are best asked on Hard-light, where they will be asked quickly and efficiently.