[basementjack]

1) from the Xbox's hard drive
2) from a usb hard drive *
3) from the network, with Windows Media CENTER as the back end **
4) from the network, with Windows Media PLAYER as the back end ***
4a) from the network, with the Microsoft ZUNE software as the back end ***
5) from the network, with another server as the backend ****
6) from an optical drive (ie internal DVD, or external HD-DVD)

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notes:

Each type of playback has certain combinations of supported file formats and types - for example you can (as of Jan 2008) play divx files streamed from media PLAYER, but not media CENTER

* the usb drive must be formatted FAT32, and files can be no larger than 4GB each
note that with xp and vista - you can't format large drives with FAT32, so you'll need a 3rd party utility to do so.

** When Media Center is your back end server - you access it from the media center option on the Xbox dashboard. If you use it alot, you can set the 360 to auto start in Media Center mode. Media center could currently be windows Media center edition 2005 (Basically XP) or Vista Home Premium or Vista Ultimate.

*** When Media Player 11 or the zune software are your back end, you access these from the Xbox dashboard under videos (not under media center)- note that neither of these back end choices requires a Media center PC

**** programs like tversity are supposed to be able to stream to the 360, but I haven't gotten it working yet...