Below script will help to drop the scalar function present in SQL Server 2005 if exist.
It is always good practice to write the drop statement before creating any stored procedure or the database function.
Lets say the function name is fn_GetFirstDayOfWeek
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[fn_GetFirstDayOfWeek]') AND type in (N'FN', N'IF',N'TF', N'FS', N'FT')) DROP FUNCTION [dbo].[fn_GetFirstDayOfWeek]