Any luck with the Samsung? I'm also trying to connect my MacBook Pro into a T220HD (with MiniDP-to-VGA adapter). It works otherwise, but it still thinks I should check the cable. See photo: http://img.skitch.com/20090228-r8sxt7esm7hs6h9hfnsu2cx6x4.png (Tarkista signaalikaapeli = Check signal cable). Isn't there any way to just dismiss that?
I've also tried this with a Mac mini, and it works fine without any annoying messages on the screen.
You've already had better success than me! I get the "Check Signal Cable" message on the screen without any actual screen pictures.
Sorry, I wish I could help further.