The video card has to be at least 32MB and OpenGL 1.4 compatible (though the latter is usually not obviously listed in a card's description, so you just have to gamble sometimes)
There's a list of supported cards at
http://www.lucasarts.com/products/sw...GI_system.html
As for system RAM, I have run it on a computer with only 256MB, and while you need to turn down some of the neat features to get the game to run smoothly, it works fairly well, so an upgrade to 512 isn't a must.
Hope that helps.