Yes. .tar.gz format as well.
I will assume the question indicates you have not had the Mac very long. Which makes me believe you might be using Leopard.
If you use Leopard, there may be a “compress” “uncompress” choice in the context menu when you, what is it called?… control (right) click?… on a zip folder. I also believe that Safari might be capable of unzipping .zip files. If not, you can Google “Stuffit”, which is a Mac compression utility that can handle .zip. Or, you could download the .tar.gz version of WordPress, open a terminal, and type;
tar -zxvf wordpress-2.7.1.tar.gz
That might extract it. I think the syntax is correct. I hope someone with a Mac will correct me if it isn’t… maybe you need to cd to the download directory first, I’m not sure.
Or you could try this:
http://www.google.com/#hl=en&q=Mac+%22how+to%22+.zip&btnG=Google+Search&aq=f&oq=Mac+%22how+to%22+.zip&fp=OlAWEoQSgPM