WordPress MU

Hi I am very new in here and sorry if I do stupid question.
I just installed wordpress-mu 2.8.4 (new install)
I set that new user can register and choise for new user name or also a new blog.
When they register as a user there is no problem
when they register with new blog and they try to activate the blog, come a white page where stay... server unreachable...
the main address is http://blog.christiansworld.org and automatically register the new blogs like http://newblog.blog.christiansworld.org
can someone help me?
thank you very much for the help.
God bless you

You need to enable wild cards for your DNS and webserver

can you explane me clearly?
I dont know what you mean

Its in the installation instructions.

ok thank you :)