Do you read German? I'm guessing that you might, so I'd start by looking at this official page from the German government:
http://www.einbuergerung.de/26.htm
Moreover, have a look at this PDF. It answers absolutely any question you might have in considerable detail:
http://www.einbuergerung.de/Einbuergerung_2006_neu.pdf
If you don't read German, you first should learn! But in the meantime, have a look at the official Living in Germany handbook, also published by the government. On the left-hand side bar, click on "politics and law". Then click on "German citizenship", although the section on "Foreigners' rights" may also be of interest. Having a quick look at the section on discretionary naturalisation, it looks like that's a possibility for asylum seekers and spouses of German citizens. But again, I'd refer you back to the brochure, "Wie werde ich Deutsche(r)" linked immediately above for complete info.
Here's the link to the manual:
http://www.handbuch-deutschland.de/book_en.html