Using other brands with Google AdWords

Hello everybody,

I appreciate your professional input regarding my previous question(s). We are a startup in Europe looking to increase our traffic through use of Google AdWords campaigns. I would like to know what the restrictions are on using the brands of competing products or companies as keywords in your AdWords campaign. Basically, how can we target users who might be customers for similar products and brands without facing legal issues?

We would first like to focus on the UK and USA, but input from other countries is very welcome!

Thank you!