It may depend on which country you hold the raffle and what you catually call it. A spaniard made headlines here when he tried to do this in Madrid, but Hacienda told him he had to pay a massive tax up front based on the value of the prize (I think it was this, someone else may clarify) Guy said it was too expensive and gave everyone their money back. In Ireland its the same as I had an owner about to do this and found the same/similar rules
However in the UK if you make it as a draw, with a clear question and charge for entry, I think you can get away with it!
Ask at the lotteries commission in the UK for more info and good luck