If you need an solution, i think i've got one.
When i put my switch on 10HD instead of auto (or 100FD/HD...), i've got no interruptions.
So try the speed to 10HD (switchsettings, an old hub instead of switch...).
I've tested it also with fixed settings on 100FD, but i had the same result. I think that the build in network card can't live with real 100 full duplex...
Before i lost connections after a few minutes. Now it runs for about 48hours without any hickup.
I monitor the camera with cacti, i poll it each minute, so quite sure that i've got no interruptions anymore...