Provided you're running Windows you can download it from here and save it to disk. Double-click the downloaded file and the font will be installed into your Windows\Fonts folder. If of course you installed Windows in a different location under a different name (Win98 or WinXP e.g.) you'll have to tell the automatic unzipper. Into the Fonts-folder it has to go.
If after installing the font and refreshing your browser window, the letters on my page are still not Greek, you may have to re-start Windows. Because the fonts in the fonts folder are initialized at boot-up, and Spionic wasn't present then, so might not be recognized yet. Or you have to press theor .Though it should already be accessible from word-processors and text-editors.