If you need a quick look at the Ethereal source code, you will only need a Web browser.
A simple view on the latest developer version can be found at:
http://anonsvn.ethereal.com/ethereal/trunk/.
A comprehensive view of all source versions (e.g. including the capability to show differences between versions) is available at:
http://anonsvn.ethereal.com/viewcvs/viewcvs.py/.
Of special interest might be the subdirectories:
trunk - the very latest source files
releases - the source files of all released versions