Homepage banned but not interior pages?

[mjvndhsb]

When is a redirect script bad? We have 3 domian names pointing to one page then one is redirected to another page on the same site, and another is just an alias for the main domain. Google seems to have penalised us recently for something (homepage is PR=0) and some pages have dropped out of the rankings altogether.

I want to have 5 websites that look different, have different domain aliases but are under the same main domain (driven by the same database).

Without a redirect how can this work? and can anyone see another reason for the site having been penalised? Any suggestions much appreciated.