If you have 2 xboxes in one house, do you have to buy two copies of the games you want to play at the same time?

Yes. Unless you illegally hack your Xbox. If you hack it you might be banned from Xbox live though.

you can play games from your hard drive
http://support.xbox.com/support/en/us/nxe/gamesandmedia/games/gameplay/GameSave.aspx
you can download one game to one hard drive without buying a second copy.

You can, but it kicks you out of the game if you eject the cd. :(

yep

You need 2 discs, you still need the disc in the xbox even if you have it installed on the HDD, the only game I have seen so far that could cheat was mass effect 2 it comes with 2 discs I think at some point tho you would both need disc 1 in the systems.

You just update the firmware on your xbox dvd-rom to the latest IXtreme firmware for your rom version. Its simple use JungleFlasher.

and then you can either download or copy the games you want to play

but you do run the risk of being caught and banned from XBLive.. they ban your mac address on your xbox not your account, its a perma ban.

google these terms and read alot

xbins
xboxscene
jungle flasher

and for irc help its irc.efnet.net channel #fw

If I had my xbox modded, couldnt I spoof the mac on the xbox?