Current Timestamp upon creating of a record

[Frank Fischer]

Hi all
 
i would like to create a Timestamp upon initial creation of a record. I
expected this could be done using now() in my INSERT statement but obv. the
related field gets actualised each time a record is updated. Unfortunately
that's not what i like - i would like to have the timestamp set just once
upon creation time without any changes later on. 
How could this be done?
 
Thanks a lot for your help
Frank