You need to do something like this:
DECLARE @NewID INT
INSERT INTO Customer(LastName,FirstName,......) VALUES(Value1, Value2, .....)
SELECT @NewID = SCOPE_IDENTITY()
INSERT INTO Employment(CID,Employer,.....) VALUES(@NewID, ValueA,..........)
SCOPE_IDENTITY: Returns the last identity value inserted into an identity column in the same scope. A scope is a module: a stored procedure, trigger, function, or batch. Therefore, two statements are in the same scope if they are in the same stored procedure, function, or batch.