"typically three raises plus one initial bet" is the rule I guess.
Poker is typically played "table-stakes" which means that a player cannot bet more money/chips than is setting on the table in front of him. The only thing that would prevent infinite reraises between two determined players is one (or both) running out of money to bet.
In heads-up play, as soon as one player goes all-in and is called (or calls all-in), the betting is over, the dealer deals the remaining cards for the hand and the players show their hands and the high hand wins. (Actually, the players' hands are typically shown as the last call is made, but I don't think this is required.)
As far as I am aware there is nothing to stop someone ten betting for example. It's all down too how many chips you have.
Its unlikely to happen, because most of the time once its gone to 3 or 4 bets then someone will go all in and the other person will call therefore ending the betting.
In limit poker there is always a cap on the number of raises, typically three to four. In Big bet poker (IE no limit and Pot limit) there is usually a cap but not always. More caps with lower limits, less caps the bigger the blinds.
The cap is lifted on the round after the players find themselves head up.
The reason for caps is because it discourages collusion.