Hi, and welcome to the forums
Winamp 5.0 is the direct upgrade from Winamp 2.9x
Winamp is Winamp is Winamp (0.x, 1.x, 2.x, 5.x).
Winamp3 is (and always has been) a separate product/player.
All Winamp 2.x and Winamp3 skins will work with Winamp 5.0
(though some freeform skins will need updating slightly for full compatibility).
Yes, the entire winamp.com site is currently being redesigned
and everything will switch over when Winamp 5.0 Final is launched.
And as Mr Jones said, when
is when it's ready. There is no set date.