lol i just looked it up. its the exact same as portal1. (cept its own source game, and not a hl2 mod)
there are no lighting modifications to the engine itself. just a few basic additions.
welcome to 2004 tech lol. in fact portal2 should run better then 1 did on any same computer. since it was created as a stand alone game upon itself.
if you couldnt handle it, you should be ashamed f your old ass computer, not sucking a consoles richard lol