How to highlight just the name (not the extension) for renaming?
Solution 1:
Use something else than Nautilus' List View mode. It works fine in the Compact View and Icon View modes. Apparently it's a regression: https://bugzilla.gnome.org/show_bug.cgi?id=627110
Update:
This is now fixed in the development version of Ubuntu 11.10 (Nautilus 3.0.1.1).
Solution 2:
When I right click a file and select Rename, or press F2, the extension isn't highlighted.
To answer your question: you don't have to do anything.