Can I make polenta out of regular cornmeal or do I have to get a special polenta mix?

Go to a good Italian deli and you will find various grinds of polenta from coarse bramata to finer lampo. Both will make polenta - just coarser and heavier or lighter and softer. Don't be afraid to approach an Italian customer and ask - you will be surprised what you can learn.

Polenta is a coarser grind than cornmeal. The cooked result is a bit different.

Regular corn meal should do. There is no real polenta mix out there, just refined corn meal for different purposes.
Try baking it into small cakes with a dollop of marinara on top. Yum.