both....
64 bit os runs on a 64 bit computer
well a 32 bit os runs on a supported 64 bit or 32 bit computer. but does not gain the extra speed due to it not using the 64 bit extensions of the system.

Vista is quite slow at the moment, particularly for games.

Some problems with beta 2 are slightly improved on in the latest development version, but for an opinion with probably more credibility:

[url]http://www.anandtech.com/showdoc.aspx?i=2805[/url]

There also seem to be some speech recognition issues:
[url]http://www.youtube.com/watch?v=cjTIe8bSpcE&search=vista%20speech[/url] :wink: