Question : Index fragmentation

I would like to know how to  check the fragmentation of a index or table

Answer : Index fragmentation

http://blog.sqlauthority.com/2007/06/24/sql-server-comparison-index-fragmentation-index-de-fragmentation-index-rebuild-sql-server-2000-and-sql-server-2005/

and for additional reading:

http://technet.microsoft.com/en-us/library/cc966523.aspx