Can anyone give me a quick run down on what I need to get VGA going with my dreamcast? Is it a physical modification I have to make? A cable?
You just need to get a VGA box. No modification is necessary, but some people have modded their system to move the internals of a VGA box into the Dreamcast itself for cosmetic reasons.
Search for Dreamcast VGA box on ebay. You should find plenty there.