Can't upgrade from woody to sarge (sources.list problem?)

[Adam Fabian <awfabian@gmail.com>]

I have Debian installed on my xbox.  It's Xebian 1.01, or something like
that.  As nearly as I can tell, it's exactly the same as woody except
that the kernel is a 2.4 kernel with xbox patches, and a backported
version of XFree86 4.3.0, and some customized configuration files.

xbox:/# cat /etc/debian_version 
3.0

xbox:/# gcc -v
Reading specs from /usr/lib/gcc-lib/i386-linux/2.95.4/specs
gcc version 2.95.4 20011002 (Debian prerelease)

Anyway, my point being that I'm pretty sure it's almost pure woody and
looks a lot more like a customized Debian than a derived distribution.

So, my sources list looks like this:

deb-src http://ftp.us.debian.org/debian/ sarge main non-free contrib
deb http://non-us.debian.org/debian-non-US sarge/non-US main contrib
non-free
deb-src http://non-us.debian.org/debian-non-US sarge//non-US main
contrib non-free
deb http://security.debian.org/ sarge/updates main contrib non-free
deb ftp://ftp.nerim.net/debian-marillat/ sarge main
deb-src http://perso.wanadoo.fr/debian/ unstable main

Then I type:

xbox:/# apt-get update
[snip]
Hit http://ftp.us.debian.org sarge/main Release                         
[snip]
xbox:/# echo $?
0
(In other words, everything appears successful.)

xbox:/# apt-get dist-upgrade
Reading Package Lists... Done
Building Dependency Tree... Done
Calculating Upgrade... Done
The following packages have been kept back
  lame liblame0 libpostproc0 mplayer-586 
2 packages upgraded, 0 newly installed, 0 to remove and 4  not upgraded.
Need to get 1145kB of archives. After unpacking 4096B will be freed.
Do you want to continue? [Y/n] 

I expected that a lot more packages would need upgrading (like, say,
gcc).

How can I upgrade?  I don't want to mess with the kernel package, so I
guess I should pin it or something.  There might be some configuration
file holding everything in place.

-- 
Adam Fabian <awfabian@gmail.com>