I'm not sure if this is in the right section, so I'm sorry if its not.

I quite often lag in game, but I've never been sure if it is graphical lag from my card unable to keep up with the game, or internet lag and my internet is freaking out, it happens pretty much everywhere.
My graphic settings are on the lowest and I get 11fps max in dungeons and about 7 anywhere else, on the otherhand my internet isnt the fastest thing out there, but I've never lagged so badly in a mmorpg before.
So i don't know if anyone can give me advice, my graphics card is a AMD Raedeon HD 5450 (i think).
I know this seems a bit all over the place, I kind of want to make sure I dont buy a amazing gaming pc only to find out its my internet screwing me around.