well first off, i want to say Congrats.
ive been running Eds Debian(Xebian) since 2007

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Now to business,
QUOTE
"i installed xebian on my xbox along-side with XBMC"
did you install XBMC Native(XBE install) or did you install it on Linux?
QUOTE
"i need to install flash player"
theres three ways to do this, all will require the use of a terminal.
1. the APT way: using the terminal, type in the following "sudo apt-get install flash-plugin", Alternatively you can SSH into youre Xbox from a PC or other Device with a SSH-client (Putty on windows, ssh on *nix)-(older versions of Xebian require you install ssh, just "sudo apt-get install ssh")
2. The web-way: you can always get a native version from the Adobe website(http://www.adobe.com/go/getflashplayer). offered are "yum" "rpm" "tar.gz" and "deb", since youre system is a Debain based system, id suggest the "deb" installation. click it and download it.
from here open the terminal, and change to the directory you downloaded the file to.(default is /home/{username} - Alternately, "~") now just put in the following "sudo dpkg -i {filename}" (or "sudo dpkg -i *.deb" if no other debian installers are in the same folder)
3. The manual way: this is by far the longest and most pain-in-the-butt route, as it requires making appropriate directory's and copying files, which personally drives me nuts, 2 steps is better than 15.
(http://www.adobe.com/go/getflashplayer). offered are "yum" "rpm" "tar.gz" and "deb", since youre installing manually, you need the "tar.gz". from here open the terminal, and change to the directory you downloaded the file to.(default is /home/{username} - Alternately, "~").
Now, theres a few ways to extract the file, i personally prefer the "gzip -d *.gz && tar -xf *.tar" route, i find it faster. it will create the file "libflashplayer.so", this needs to be in the following folders for firefox and/or other apps to use it.
/usr/lib/firefox/plugins/
/usr/lib/mozilla/plugins/
the easiest way is to place it in "/usr/lib/firefox/plugins/" and symbolic link(ln -s) the file in the "/usr/lib/mozilla/plugins/" folder.
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QUOTE
"i need to figure out how to keep the screen from running off the sides of my tv"
thats a Overscan issue, as i use Composite cables(HD-Cables) i dont have that issue, im sure some one here can give you a hand on that, but i will continue to look for a solution for you!