yeah you can...
I recently reformatted my desktop and picked up XP MCE, it works great, I don't have a Tuner in that PC either so it's not necessary. The Media Center interface is very slick (has the same fluid motions as the dashboard) The only thing I dont like about it is it's not configrable enough and trying to find options to set it up how you like is difficult. I spent about 20 minutes just trying to specify which folders I wanted it to grab it's MP3s from instead of auto searching my entire computer...

But on a whole I like it, and running the Extender is like remote admining into the media center interface, very cool...
as for transfering files to your Xbox 360 HDD from an external HDD... no you can't do that. files on the 360 HDD can come from 3 places
-Created by the Xbox 360 (like save games)
-Downloaded from Xbox Live
-WMA files ripped by the Xbox 360
THATS IT.
Wow. Thats a very detailed reply. Thank you so much.
I'm currently running WinXP HE. If I plan to install MCE, can I just upgrade? Or do I need to reformat my HD?
. I've been looking for this informatoin for a long time!