If it is a custom list you can define which fields are going to be available on each form using the attributes ShowInDisplayForm, ShowInEditForm and ShowInNewForm.
http://msdn.microsoft.com/en-us/library/aa543225.aspx
I usually use them when im define the content type.
<FieldRef ID="{493AE2E2-DA5D-46C6-93D9-D43F85B03329}" Name="myCustomField" Required="FALSE" ShowInNewForm="TRUE" ShowInEditForm="FALSE"/>
i hope it helps!