If the paint you used is water based, you should be able to wet it and rub it off. Even if you spilled a can of it on the floor, this should work.
At any rate, you can try cutting a piece of soft plastic, like a lid from a plastic container, and just scrape. The tiles are fired and glazed and scraping shouldn't hurt them. As far as what to do about paint that's gotten in the grout, you'll probable have to do your best at cleaning it, and at worst, re-grout. (Not a pleasant thought.)
If you have more to add, post up. My best to ya and hope this helps.