Hi Keith.
In SQL2000, you can create a user defined function. An example would be:

CREATE FUNCTION add_columns (@number1 int, @number2 int)
RETURNS int
AS
BEGIN
RETURN (@number1+@number2)
END

To use this as a calculated column, open the design window for your table in Enterprise Manager. Add a new column and use the 'formula' property to call the function like this:

([dbo].[add_columns]([column_name1], [column_name2]))