the file format is .dmg as it is a Mac file. This tool is designed to be run form Macs and injecting onto other systems via VNC. This will be the first part to enable it to work in your scenario.
It will not work if you are trying to install the tool on a windows box.
Neill is correct. Eggplant runs from a Mac only. If you do not have a newer Mac, you absolutely cannot run Eggplant.
As for testing your application... If you can set up a VNC server on your Sun Solaris box and can drive the application through the VNC connection, then Eggplant will be able to test your application (at least on a very basic level).