Before setting out to make your fortune from poker that's a very serious question to ask yourself. DO I NEED TO PAY TAX ON MY WINNINGS? Nobody ever REALLY wants to pay tax, but unfortunately in life only 2 things are certain - and one of them is taxes. Saying that it's not just a simple yes, it depends on where you live.
If you live in the US then yes you will have to pay tax on any poker winnings. Their is some silver lining in that before paying your tax you'll be able to deduct any losses you've made. In that respect it's not much different from any other business, profit-loss and pay tax on the balance.
In Canada it's a different story. Taxes on poker winnings are going to be deducted at source i.e. you're going to get less in your pocket. Any losses you make elsewhere have to be claimed back, it's much more of a "take it first and you can beg for some back" attitude from the government. Nice.
The rules across Europe vary quite a lot but where is regarded as the best place to setup shop is the UK. Poker winnings are not taxed in the UK and for this reason a great many of Europes very best poker players have started to move. London has so many major touraments (including a lot of TV tournaments) that it's a no brainer not only in terms of tax but also having the chance to play as many big games as possible.
Disclaimer - Whenever you mention anything about tax people can go off on one. The information above is as we have been informed and believe to be true, however we can't guarantee its accuracy. Don't be stupid, before changing anything that could affect your tax circumstances talk to a qualified accountant!