We have linux Cent OS. since we installed alfresco 2.1.1 Enterprise edition.
Now for our two projects can we use same alfresco for different configurations for DB and running instance ? Can we do like thing to changing the port.
You can change the 8080 port for the WebUI in the tomcat configuration. Look in tomcat/conf/server.xml, and change the port number defined on the Connector (just search for 8080 in the file).
The smb port is slightly more tricky, and I'm not sure how you'd get around that without using multiple IP addresses (give the machine two IP addresses, and bind both Tomcat and CIFS to a particular address), though someone else might know. You'll also need to ensure that both are configured to point to different databases in the DB config.
The above assumes two installations of Alfresco running on the same machine, rather than a single installation. If you want multiple instances running in the same configuration, have a look at http://wiki.alfresco.com/wiki/Multi-Tenancy in the latest versions, which may do what you want.