You can get the latest copy of the program from the Ethereal website: http://www.ethereal.com/download.html. The website allows you to choose from among several mirrors for downloading.
A new Ethereal version will typically become available every 4-8 weeks.
If you want to be notified about new Ethereal releases, you should subscribe to the ethereal-announce mailing list. You will find more details in Section 1.7.4, “Mailing Lists”.