No More DBCC SHOWCONTIG

In SQL Server 2005, DBCC SHOWCONTIG has been replaced with the function sys.dm_db_index_physical_stats. Use this function if you need to diagnose fragmentation and page usage issues.

Pay attention to the fragmentation levels in the output. This is reporting more accurately than in SQL Server 2000.

Here's a Books Online link explaining the new function:
http://msdn2.microsoft.com/en-us/library/ms188917.aspx

And a link on index fragmentation:
http://msdn2.microsoft.com/en-us/library/ms189858.aspx