How do I update a custom thread field on editpost?

[AreaZeroOne]

Hi.

I created a custom field, i'll call it, Field1, that a user fills out when creating a new thread. Now i've written some plugin code so that when the new thread is created, the field1 options (option1,2,3,etc are sucessfully posted to the db (along with everything else).

However, i'm having trouble understanding the rest. On editpost, I can populate the field with the current selection, but I cannot update the field (one because there's nothing handling it). I'm pretty much stuck here!

So to avoid further insanity, how would I go about finishing this up?

Thanks for any help.

:edit: The fields have nothing to do with the fields one can create via the AdminCP.