How to give a user only select permission on a database

You could add the user to the Database Level Role db_datareader.

Members of the db_datareader fixed database role can run a SELECT statement against any table or view in the database.

See Books Online for reference:

http://msdn.microsoft.com/en-us/library/ms189121%28SQL.90%29.aspx

You can add a database user to a database role using the following query:

EXEC sp_addrolemember N'db_datareader', N'userName'