I just read your message and I dont know if you already find your biological father, but I wanted to say that there is a website called www.extrakoll.se
where you can look for people´s tax information in Sweden. The good thing with it is that you can see when they are born and they partial current adresses.
I looked for the name Peter Lindgren but I did not find anybody born around 1965 in Stockholm. It can be that he moved to another city. You can try it yourself doing an advanced search.
I hope it helps.