just type into google *windows 7 torrent* check the torrents comments before downloading.
Always best off doing a complete clean install, although you can just install it over your previose o.s i think it would just create a partition and when you boot windows up you can choose which o.s to use if i rightly remember. You won't lose your files that way but i'm not sure it would run faster either, i'd recomend a complete clean install and just back your files upWhen you install Windows 7 do you lose all your saved files ? Will it just cover Vista or will it remove Vista and run faster?