Multiple urls to Single Blog

I am trying to allow a single subdomain install to have more than one url point to it. Example:

sample1.domain.com
sample1.com
http://www.sample1.com

all point to

domain.com/sample1

I believe this has been addressed before and involves changing a single line in one of the .php files for either domain-mapping or multi-site. For the life of me, I can't find it after reading it earlier this week.

Thanks,

MLO