Yes, tech is the same for Mac as the PC. The only way to get any HD signal to display in HD on your computer is to install an HD tuner that will pick up your local over the air TV stations that are broadcasting in ATSC format. You can get other devices (Ex. I have my HD satellite receiver connected to my PC) to connect, but it will require additional hardware. Typically this will be either a video card for a desktop or a TV tuner for either desktop or notebook.
This is where the fix is in, no manufacturer builds any way to connect a HD source to either of these two pieces of hardware. I have not found any third party manufacturer either. The best you have is to connect via coaxial, composite or S video.
I can tell you I have my HD satellite connected to the TV tuner on my PC via an S video connection. No it's not HD, the signal is reduced to probably 480 (i probably, don't remember). It does maintain it's widscreen aspect and there is a difference in the picture between this connection and the component connection that goes straight to the screen. However, it's as good as any other non HD signal.
This would probably be your best bet to get your xbox 360 to display on you laptop screen. I know the 360 has composite connections which will not be as good as s video (at least don't think it has s video, didn't go look at mine).
From what research I've done in last couple of weeks, looks to me like elgato.com is making the best hardware for the Mac at this time. You would just need to check out which of their tuners (did see one) would provide you the capability of this type connection.