how to understand Blocking Problem in SQL Server 2005 and how to find solutions?
Go through the articles that others have suggested.
Blocking can happen due to multiple reasons.
For example, if you've run a update statement on a table which is taking long time and other user is trying to perform a DML query, this scenario will cause blocking.
Blocking may also happen due to I/O.
There are some DMVs in SQL Server 2005 which will tell you whether there are blocking present or not
sys.dm_os_waiting_tasks is one of them...