different domain with different gust setting

[pishtazweb]

hi
in my forum i have 2 active domain domain1.com and domain2.com both of then would show one forum with on sql.
i want to do setting like this on it:
1-when gust type domain1.com can see forum and must log in on forum on the other hand i want to search engine cant reach to domain1.com
2-but i want to guest can see whole forum on domain2.com and this domain is optimize with search engin.
how can i do that?