SQL Server Create Triggers

Please somebody help me with the following:

I need a insert / update Trigger for table[ActionType] column name is [actiontimestamp].

Trigger will insert the current timestamp into the column.  Only on Insert and update.



Here is my table and the columns just incase:
CREATE TABLE [dbo].[ActionType](
                [id] [int] IDENTITY(1,1) NOT NULL,
                [long_type] [varchar](30) NULL,
                [dc_id] [varchar](5) NULL,
                [Backups] [varchar](max) NULL,
                [dateofincidence] [datetime] NOT NULL,
                [actiontimestamp] [timestamp] NULL
) ON [PRIMARY]