How do you create a new copy of NewForm.aspx in SharePoint Designer 2010. I would like to the customize the copy. I tried to copy the source code from the original to a new New Item Form, but that seemed to erase the original. Or, is there is a way for me to add fields to the New Item Form. Thank you.
Alternatively you could use the browsing mode of SharePoint Designer and, at your preference, copy/paste or Ctrl+drag the NewForm.aspx file within the list's (or document library's) root (or Forms) folder. Then you could rename the files and in the list's properties choose the default item creation form as well as item display and item edit forms.
My personal preference is to create a new form from scratch -- leaving the original intact. To do this, browse to your list in SharePoint Designer 2010, then click on "New" in the Forms list on the right. It will ask you if this new form is for "New", "Display", or "Edit" and allow you to set the default form for each action.
A little additional info here. If you want to customize the form (e.g. hide certain fields or change the order of the fields), I believe it is much easier to do that using a Data View Web Part on your New page or or a custom "Site Page."