Welcome to this forum!
Watching movies from shares in your network is an often discussed topic in here and not really ATV specific. Using the search function should reveal lotsofposts.
Using an USB stick with your AppleTV requires currently additional modifications. A good place to get more info about this is awkwardtv's wiki
Always read the XBMC online-manual, FAQ and search the forum before posting.
Do not e-mail XBMC-Team members directly asking for support. Read/follow the forum rules. If you don't have the time to read them, please don't take the time to post in this forum!
For troubleshooting and bug reporting please make sure you read this first.