A laptop video card can't usually be changed. And even when it can, the card that came out would only work in exactly the same model laptop.
I doubt he took your video card.
As Chris pointed out, its more likely he swapped RAM. Right click "My Computer" (its in the start menu if its not on your desktop) and choose properties. Select the general tab, see how much memory you have, and then look at your original receipt and see if it matches.
Anti Virus programs can make your system slower because they typically sniff every byte of data that is moving around the system. They sniff all network transactions, every file you or the system touches. I suggest you remove it and see if the speed returns. If it does you have your culprit.
I run AVG on my Windows PCs, as an individual you can get it for free:
http://free.avg.comIn my experience, AVG does not steal as many resources as Norton or McAfee.
You can also see how much memory McAfee is taking by pressing CTRL-ALT-DEL (once) and choosing the Task Manager. Then look on the processes tab and see how much memory its taking. On my Virtual Machine here at work McAfee is only taking a few megs.
You should also consider that McAfee might be running an automated scan, that will severely slow down even the fastest of computers. You should be able to check that status by hovering the cursor over the McAfee icon on the right side of the task bar.