I get asked this offline a lot too and will give you the same advice.
If you lived there or went every weekend I'd say get snow tires. If it's an occasional thing, I've been fine for years on good (actually good, not just with a lot of tread) tires. Tirerack will help with ratings.
That said, the Killington access roads are no joke. With AWD going up is not the problem. Going down can be scary. They maintain them pretty well but if the weather is bad I'd stick to the main road and not the East Mountain Road shortcut.