I need to point
How can I do that?
You cannot do this through etc hosts. You are mixing up 2 different protocols here, http and dns. /etc/hosts will help you redirect admin.company.com to 192.168.2.100, but you need to the redirection to /admin on the web server.
If you are using apache you want to likely used named virtual hosts
This article outlines this: http://httpd.apache.org/docs/1.3/vhosts/examples.html