Kyiv, November 2010.

Could you please tell me if anyone can participate in this tournament, or are there any qualifying rounds or skill checks? Please provide detailed rules. I might join – I play decently, although I haven't played with pros before.

This tournament is actually a qualifying round, so all you need to participate is desire and love for the game. Well, and a willingness to follow the tournament rules. Even if you don't perform well due to a lack of experience in online tournaments, you'll still gain invaluable experience and a lot of new impressions.
For example, I became reasonably good at Heroes after participating in a club tournament in St. Petersburg.
There are all sorts of people among Heroes players, but I haven't met anyone who wouldn't share their knowledge and experience with someone who wants to learn (although the way they explain things can sometimes be quite peculiar).