I use Maya 7 & 2008 on my iMac with no problems. I also use Maya on a Macbook with integrated video, with no problems either. Besides, the viewport wouldn't be lagging this much if it was just a video issue. There is one way to check however. When you rotate your scene, press the spacebar. If the view updates to the proper position when it goes to the four view layout, it means its a redraw issue with your video card. If it doesn't however, and just hangs, or does what it usually does, then it's something else. Reinstalling may help. Make sure you delete the preferences as well, as these are not deleted when Maya is uninstalled.
Also, make sure to run software update, and see if there are updates for your video card.
Hope all goes well!
Imagination is more important than knowledge.