There is a second, legal grey-area option. For years, the official port was broken, so the community fixed it. is a mod/launcher that takes the original Halo 2 Vista files and completely strips out GFWL, adds server browsers, and allows LAN play.
Purchase the Master Chief Collection or the individual Halo 2: Anniversary DLC . Halo 2 Pc Game Download LINK
That being said, here are some legitimate options to obtain Halo 2: There is a second, legal grey-area option