The big question here is if you also own a license for Max for Live.

Installing M4L is easy; you install Max5 onto your computer after which Live will automatically pick it up (that is; if you installed Max to its default location).

If you installed Max5 to another location then simply pull up Live’s preference screen, go to the "File Folder" tab and point the "Max application" entry to your Max 5 installation directory.

Keep in mind: owning a Live 8 and Max/MSP license does not entitle you to using Max for Live; you need a separate license for that as well.