Access SQL Server catalog

Sometimes, you need to know schema in details of your database. You may use system objects such as sysobjects/ sys.objects, syscolumns/ sys.columns, etc or system stored procedures to query that information.
Another way to get that information is using INFORMATION SCHEMA in SQL Server 2005:

View	Contains information about
COLUMNS	Columns accessible to the current user in the current database.
INDEXES	Indexes in the current database.
KEY_COLUMN_USAGE	Keys in the current database.
PROVIDER_TYPES	Data types supported in SQL Server Mobile.
TABLES	Tables accessible to the current user in the current database.
TABLE_CONSTRAINTS	Table constraints in the current database.
REFERENTIAL_CONSTRAINTS	Foreign constraint in the current database

Source: SQL Server Book online
For example:
If you want to know the schema of tblEmployee Table, you can query like that:
SELECT * FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'tblEmployee'