I have a
domainname.com and want to redirect it to Google Apps,
sites.google.com or iGoogle via the CNAME.
How can I achieve this?
Try following the instructions on this link: http://www.google.com/support/a/bin/answer.py?hl=en&answer=47283
There are many ways you could redirect a domain name to another domain name.
One ways is to use your domain manager dashboard. If you have GoDaddy just log in there and click on set up DNS.
Other way is via htaccess.
There are more other ways.
Google sites has a help document that answers this question for you.
The basic steps are: