Modify webpart editor zone not visible

Question

I made a customization to SharePoint 2007 by using a ready made minimal page I found from web. Everything works fine except I cannot modify the webparts I added to content pages. When I click Modify Shared WebPart menu item from the webpart menu, the webpart properties editor that we always see on the right side of the page doesn't come up. I think I should add it to my page layout in some way but how?