MW2 haven't got mod support, as COD4 has.
Also, all cods doesn't run on the source engine (they run on ID tech 4, as far as I know), therefore it wouldn't work to put those mods in your sourcemods folder even if MW2 had mod support.
However, some "hackers" have done a incredible job on making MW2 as it was supposed to be (mod support, dedicated servers, new maps, in-game download, developers console, etc), take a look at alterIWnet • Modern Warfare 2 enhancements, dedicated servers and more.
But yeah, it's a cracked version of mw2, but it's not illegal if you've got the original game + the dlc files.