I had a big post with links and everything about the differences between liberalism and libertarianism, but a fuse got blown and I lost it. Oh well.
Liberalism and libertarianism are different, as Johnny C pointed out. Libertarianism is, crudely put, the concept of free market capitalism applied to politics. They put heavy emphasis on civil liberties and are alike liberals in that regard, but are conservative fiscally, and believe in limited (way limited) government, and are alike conservatives in that regard. As a result, your average libertarian might be pro-choice, but pro-gun rights. They're against the Patriot Act, but also against anti-discrimination laws and hate crime legislation. They are anti-social programs and anti-regulation.
The current libertarian candidate for President of the US is Ron Paul, who's jockeying for the Republican nomination, unsuccessfully. Paul is notable for his campaign promises to dissolve the federal reserve, remove the United States from all international bodies and build a mexican-proof fence along the border. He's also voted against civil rights legislation, though I'll have to dig a link up for that, and he's very vocal about his distrust of young black folk. In my humble opinion, the man's a fucking nutjob that should be kept as far away from the presidency as humanly possible. But he has his fans.
As for Ayn Rand in all of this, it's a bit erroneous to call her a libertarian, she wasn't one, technically. But she's well regarded among libertarians for her ideals of individualism and capitalism.