The most important Polish tribes are Polans, Masovians, Vistulans, Silesians and Pomeranians.
I'm not a historian but I've read a few times that the stories about the Polans, Vistulans etc. seen to have been invented by 19th c historians who cared more about strenghtening the sense of national identity than about historical truth.
Certainly there were Slavic tribes living in the territory of today's Poland, some of them quite powerful and significant, especially in the southern part, Wiślica being the biggest centre of power for a couple of centuries. It remains a mystery though why the centre of power shifted to Gniezno in the 10th century and how the process of unification went. There are also a lot of mysteries concerning Prince Mieszko, even his nationality (or ethnicity, if you prefer) is not clear. There are theories that he might have been a Norwegian Viking, or closely related to them.
How do Polish people view the period before then, I know something of the Bronze age and Iron age but not a lot about immediately before.
Barney, there are no written sources from the period, all we have is legends and what the archeologists manage to dig up. So it's not clear at all. Some hints are concentrated around Wiślica in the south, some other in Wielkopolska (Gniezno, Biskupin, the Gopło lake). Nobody knows what was really going on there. At school we were taught the stuff about Polans, Vistulans etc. - what Pawian wrote above, but the present date historians hold most of it in serious doubt.
Anyway, it's very probable that there existed a strong and prominent tribal state in the south of today's Poland. Some serious digging in the Krak Mound (Kopiec Kraka) in Kraków could perhaps explain a thing or two.