Unfortunatly targa (.tga) was one of the file formats removed from photoshop elements 11.
(under Upgrade Notes)
You could copy the Targa.8bi from the pse 7 plugins folder:
C:\Program Files (x86)\Adobe\Photoshop Elements 7.0\Plug-Ins\File Formats
to the photoshop elements 11 plugins folder:
C:\Program Files (x86)\Adobe\Photoshop Elements 11\Plug-Ins
I tested it on a windows vista machine and it seems to work in the pse 11 editor, though you still won't be able to import
the targa files into the pse 11 organizer.