Problem creating extended IDOC

Hi Experts,

I am currently working on CRM 5.0. I need to create segment and attach it to the standard basic IDOC type CRMXIF_PARTNER_SAVE01. I am able to create segment in WE31 but i am unable to add that to the basic standard IDOC type.

It is displaying message "Action is not possible for generated idoc types".

Is there any other way to add this segment to the standard IDOC.

It will be great help if u can send me some documents on this...

Thanks,

Samm