I have a (silly? )question for you about pagerank. If i link to a site with PR 0 this will affect my site's pagerank (=4)?
No it will not. But is it PR0 as in white bar or PR don´t- touch- with- a- barge- pole as in grey bar? If the site is PR0 it is probably only new. If it is relevant to your theme and of interest to your visitors - go for it. Support that newbie guy. He may be tomorrow´s Shoemoney.
as said above. also do a quick search site:site.com see if google has them indexed. also can do a whois seach and see if the domain is blacklisted as a spam source. Also remeber you was once too pr 0 if the sites related and usefull for your visters then link to it.