Using Data List values in Share Form

[sbixsbix]

Hi all,
probably this is a "more than an already seen question" but..
I would like to use the values stored in a datalist as a drop-down list to set some fields in creation/edit content form.
In example "product id" coming from the Products data list
Have I to write a custom field-validator?
Are there some well expalined example of a such thing?

Thanks a lot

[joseantonionava]

Crystal clear now...

We were wrong with the forms structure in config sections.

Thank you very much for your help.