duplicate content with country domains

[Istvan]

I hope to learn more how google might act in the following situation:

Since a few years my main site has a PR4 and is listed with an .at domainname. A few months ago we purchased an .de domainname, and placed the exact same site which has the .at content on that .de domain. Plus we have 2 subdomains at the .at domain. Those subdomains use the content which resides at the main-domain (.at).

The problem which we have now, is that at the .de domain we got a PR0, and also a PR0 for one of the two subdomains under the .at domain. After some research I came across, we probably ended up have a penalty for duplicate content.

Now my question is: I will now change the content for the 2 subdomains at the .at domain and I will also alter the content at the .de domain. But.. Will Google also penalize the main-domain .at, which still has a PR4?

And in what extent should I change the content, is it only the filenames, foldernames, rewrite some texts? Is there a minimum level which is considered "enough change for not being duplicate content"?

[instand1]

We have a domain with our brandname and .de and .com and they are identical (Redirect) since the beginning, at least 5 years ago. We never bothered to get the .com into the directories, so only some stray backlinks direct at .com. Initially therefore .com had PageRank 0, but now it has PR5, just like the .de.

I think that Google has found out that the sites (with different IP-number) are identical, but there was no intention on our side to push both into the SERPs, indicated by the majority of links going only to the one and no interlinking between both sites. Therefore no penalty, but also no double showing in the SERPs.