> I have a laptop with the above graphics card. The laptop has VGA and S-VIDEO
> I have read that the X600 supports DVI, but how? Is some sort of dongle
the X600 does support dvi, my agp card has a dvi port, but I think you'll find to save port space which is limited on a laptop that they will have dropped the dvi port, thinking as an occasional secondary monitor a vga port will suffice.
To be honest its hard to tell the difference in quality between dvi and vga so I wouldn't worry about it.