You need to download two files to successfully download VisIt on any UNIX computer, including MacOS X. On MacOS X in particular, some Web browsers can corrupt the VisIt binary distribution, which is the file that you download that ends in ".tar.gz". Be sure that your web browser downloaded the binary distribution properly by checking the checksums. You may also have to manually change the visit-install script so that it has execute permission. Once you've completed those steps, the most common cause of errors during installation on MacOS X is the visit-install script's inability to gracefully handle installation paths that contain spaces. Many of the MacOS X installation paths such as /Applications can have a volume label prepended to them. Volume labels often contain spaces. If you are having trouble installing VisIt on MacOS X, the easiest way to make sure that the installation succeeds is to install to your home directory. Assuming that you have correctly downloaded to the two requisite files, you can usually follow these steps to install VisIt.