[quote=Maxim]
For that matter, what's the difference between a LMG and a SMG? (I don't play a lot of fps games :P)
[/quote]

Raen's explanations are fine, but here are some images to help drive it home.

[url=http://img3.redwolfairsoft.com/upload/product/img/MG-006-K-1L.jpg]LMG[/url]
[url=http://www.arsenal-bg.com/images/defense_police/9x18smg.jpg]SMG[/url]