MySQL:

CREATE TABLE polls (
	id INT NOT NULL AUTO_INCREMENT,
	name VARCHAR(200) NOT NULL,
	description TINYEXT,
	vote_starts DATETIME,
	vote_ends DATETIME,	
	enabled TINYINT(2) DEFAULT 1,
	PRIMARY KEY(id)
);

CREATE TABLE poll_questions (
	id INT NOT NULL AUTO_INCREMENT,
	poll_id INT NOT NULL DEFAULT 0,
	question TINYTEXT NOT NULL,
	PRIMARY KEY(id)
);

CREATE INDEX parent_id ON poll_questions (parent_id);

CREATE TABLE poll_votes (
	id INT NOT NULL AUTO_INCREMENT,	
	option_id INT NOT NULL,
	post_date DATETIME,
	PRIMARY KEY(id)
);

CREATE INDEX option_id ON poll_votes (option_id);

CREATE TABLE poll_options (
	id INT NOT NULL AUTO_INCREMENT,
	question_id INT NOT NULL,
	option_text VARCHAR(160) NOT NULL,
	PRIMARY KEY(id)
);

CREATE INDEX question_id ON poll_options (question_id);