In addition to June7's comments: (I don't use macros, either - only VBA code)
You will need to "roll-your-own" to have a field like that. But it will have to be a text field - not a good choice for a PK. You can still create the special number ('INP0001'), just don't use it as the PK.
The autonumber type is not meant to be "descriptive" or have meaning, it is only meant to be unique. If it is an autonumber and the PK, it cannot be "entered" multiple times; it cannot be "entered" at all. Access enteres the number - you cannot.
Users should
never be allowed access to tables. All data entry should be via forms.
If you are using look-up FIELDS in your tables, you should get rid of them. See
http://access.mvps.org/access/tencommandments.htm Read #2 and follow the link.