Domain Mapping

Hi, I am using wordpress MU 2.9.2, and i have primary wordpress blog address is like something.domain.com and now i want to create a blogs like test1.otherdomain.com , test2.someotherdomain.com so on …

so is it possible cause every times it appends the primary wordpress blog name like if i have created test1.otherdomain.com it will create
test1.otherdomain.com.something.domain.com

and if i edit this to what i wanted , than log in and other functionality are not worked for that blog.

Is there any guide available for this kind of stuff in wordpress mu,
please help me regarding this.

Thanks in advance
Regards
Sudhir