Is there an easy way to get the flashlight working with Portal? I don't really want to have to code anything since I only want it for one map. Its just that I want some dark shadow areas to contrast with the bright areas in regular portal, but then you can't see anything because there's no flash light. Would it work if I just binded it to a key?

To use the flashlight you need to have the hazard suit, I believe....

Unfortunately, the flashlight doesn't seem to work, even with the suit. The command should be "impulse 100", but it seems to have no effect in Portal.

Impulse 101 gives you everything possible in half-lfie 2 and portal.
sv_cheats 1 enables these codes.
give item_suit will give you the hazard suit, dunno if it would work in portal though.

impulse 101 is the "give all" cheat.

impulse 100 just turns the flashlight off and on.