utorrent and teredo

Hi,
I have Windows Vista Home Premium SP1 x64 and today i installed uTorrent 1.8
( stable ).

When I open it ( utorrent ) and I look in "Options -> Preferences -> '
General '" the <Install IPv6/Teredo> button is disabled. Why? Is "teredo"
enabled by default since I installed the OS?
( I am connected to the Internet by a router through Wireless as connection
type. )

The think that pissed me off was that the "Teredo" address apearred in
"Resource Monitor"-"Network" only after I installed uTorrent... and since
then sometimes it is not active but sometimes is active even if my uTorrent
software is closed ( in "Network" tab from Res. Monitor ).

Thank You.