How to add domain to WP Multisite?

I just setup WP Mutilsite. Now I want to add each domain for each site like this:

maindomain.com/site1
maindomain.com/site2
maindomain.com/site3

I tried this: http://ottopress.com/2010/wordpress-3-0-multisite-domain-mapping-tutorial/ but failed.

Please help.

Thanks.

 

I'm also looking for the same answer for my new WPMU site. if any one have the answer please reply to this thread.

 

I just purchased a new dedicated IP address, but still can't configure it.

 

You have to make sure that your wildcard is set. If you don't have dedicated hosting, or access to set it yourself, you would likely ask your hosting provider to set it for you, provided that they do offer it.
To the OP, assuming that you have set your settings to create as folders (yourdomain.com/newsite) and not sub domains (newsite.yoursite.com. You would have done this in the set up.