Windows Vista Ulitmate is it worth it?

I am currently thinking of getting the Ultimate Edition of Vista.

Here is my question/s,

- I have been hearing that it runs games slower then XP...is this true?

- Is it better to buy Windows XP and get the Vista Ultimate upgrade? Will this save money? ( Since my XP is - you know ;) ) Considering I'll then have Win Xp and Vista- and use Win XP to fall back on in regards to the question below

- Does Vista infact not let you download shared music and videos from person to person applications like Limewire or Bit Torrent and sites?

- Finally, is it possible to have both OS's on the same pc, like on in dual boot etc, without Vista affecting the Win Xp OS and not allowing me to have shared files, music, movies, torrents etc. 

Am I better sticking with XP or what?

Thanks.