One of the websites is about cartoons (Approved.) The second one is about TV Shows (I would like to put Ads on it.) The Last One is about Software (I would like to put Ads on it too.)
Yes, you can have use account for as many sites as you want. Just read the terms of service. You may want to set up one or more adsense channels for each site so that you can track your success.
Google don't allow Invalid Clicks and Impressions Encouraging Clicks Content Guidelines Copyrighted Material For More Read this https://www.google.com/support/adsense/bin/answer.py?hl=en&answer=48182
You can use the same adsense for your other sites. Like others mention do read the tos and rules. Google is pretty strict. People often wonder why they got banned by adsense. Often times it's not abiding by their rules and terms. If you understand them and follow them you will be fine.
That was a nice question thank you for your responds guy. If there's something else I should do let me know.