eth0 keeps going up and down

[Sean McMahon]

As the subject implies my eth0 keeps going up and down.  typing 
/etc/init.d/networking restart causes my system to make a proper dhcp connection 
with my router.  Other systems are connected to this router using ethernet and 
wireless.  examining /etc/network/interfaces, eth0 is specified there inet dhcp. 
This system was working fine 2 weeks ago but now I have this problem.  I have 
been able to upgrade the system using apt-get -u dist-upgrade, both before the 
problem started and sinse the problem first occured.  ssh has a real problem 
with the up and down behavior.  It's literally happening every few seconds or 
so.  What else should I look at?
specs on system:
debian sarge with a custom 2.6.11 speakup-enabled kernel It was unable to 
connect to us.debian.org as of about 9:30AM. MST today.
let me know if you need more info
Sean