I am a Emacs newbie. I have to trying to search on how to use Emacs for use with large C++ projects particularly to index code and auto-complete function names and behave Eclips
I use CEDET with autocomplete successfully. Basically, autocomplete is the drop-down box provider, and it takes its sources from various things, most interestingly from CEDET (but also from etags and Gnu Global, which I recommend too).
A good starting point for CEDET is http://alexott.net/en/writings/emacs-devenv/EmacsCedet.html
Alex Ott's emacs config is there: https://github.com/alexott/emacs-configs -- it's an useful resource.
Note that you'll need to grab CEDET from bzr, and install/configure autocomplete correctly. I strongly recommend el-get to install autocomplete (and some other stuff too). You'll need to set up generic projects for EDE to have autocompletion working for random C/C++ files not part of a structured EDE project.
You'll have to spend some time to configure emacs, but it pays off. The tool is amazingly productive once set up correctly.