can I buy a car with my credit card

Your best bet is to get cash advance against card. Check cash advance interest rates first,might be over 30%. Take cash when buying car and stay away from car dealerships. Dealerships are professional swinddlers,they will make maximum profit from sale. In short you will pay twice the amount for car,than if you bought it from private individual.

And four times that if you take a cash advance off of you credit card.

You might convince a dealer to accept a credit card for the deposit but not the whole purchase price (unless the car is under $5,000 or so). A credit card is not your friend here anyway since their interest rates are far above a typical car loan. Dealers don't let you use them because it typically costs them 1% of the transaction value. I suspect your motivation is to cash in on the rebates offered by current cards that give you "cash back". From a dealer's perspective, he is loosing money and you are getting it. In the end, ask.

Unless you are very wealthy and well known I doubt it. I am pretty sure that even if your credit limit is high enough, most car dealers will not accept a credit card for payment.