Insert a WebPart in SharePoint 2010 list form
If you need to add custom JavaScript to SharePoint 2010 list form just like in 2007 (for example the SharePoint Cascaded Lookup), you’d need to insert the Content Editor WebPart to the same form. There are couple of ways to do it. Here’s one:
1. In a SharePoint List View select the "List" tab in "List Tools" tab group:
2. Select "Form Web Parts" and select "Default New Form" or "Default Edit Form".
From here on you can add webparts and edit their properties like in any other page.
Thanks this is helpful. Very Helpful Post. Thank you.