You should keep in mind that there is nothing to worry about as far as I know. By the end of last year, 2006, Final Fantasy XI online was available for download from Play station store and you needed some free disk space to run Final Fantasy XI online correctly. Free disk space was around ten gigabytes. As far as Windows Vista is considered I think that issue was resolved in March this year. Before that Windows Vista was not compatible with Final Fantasy XI online, but now that problem is fixed. As you can see, you have nothing to worry about.