Do you have a computer you can try the monitor with, or onboard video out? Could just be the monitor. The flicker is pretty common when using LCD displays over vga tho.
I have an LG monitor (1920*1080@60Hz) connected to vga on a 8400GS as well and I don't get any flicker; tho using the onboard video it does flicker somewhat. No flicker over vga on my ASUS VW246H (1920*1080@75Hz)connected to a Radeon 6670 either.
Okay so I rechecked - I have the VE228DR, which does not come with a HDMI-socket. The guide that came with it is for the VE228xR, which does. So is it really necessary to run it via HDMI if it doesn't even have the port for it?