Nearly the same thing here. VIA KM266/VT8375 I also loose the video signal as soon as X is loaded. I also switched to "vesa" driver & performed a HD install with no problems. The fact that your Apple monitor worked is interesting. There must be something easy that can be tweaked. I also messed with XFree86Config-4 for hours & tried the driver from probo as well, no luck.

19" Gateway monitor is properly detected, etc.

Should we move these posts to the Hardware section perhaps?