They have a free tool and a paid subscription. The paid subscription make building big categorized keyword research simple. To bad they changed their subscription, they eliminated the day and week option. If you have a lot of keyword research to do it's handy, but I could get my keyword research done in a day. Kinda irks me to have to pay for a whole month.
Seriously, why don't you just go to wordtracker.com? Wordtracker is another keyword tool. They also have a keyword question tool that works really well when picking out article topics.
Wordtracker is one of the most popular keyword analysis tools being used today. It offers a massive 340 million keyword database from which you can find out what your target audience are entering into search engines and how many times each keyword has been entered. Wordtracker combines both a respectable search term database with tools that make mining the information easy.
Word trackers is the tool help us to find right keyword. Right keyword help to find out huge traffic on your site.
Word Tracker is a paid keyword research tool. It also provide 7 day trial service. I never used it but you can check this from here: wordtracker.com/trial/