I can´t watch movietrailers on Itunes movietrailers. It tells me to download Quicktime but I already have Quicktime in Mac OS X? I can´t update Quicktime either?

Mac OS X 10.6 includes QuickTime versions 10.0 and 7.6.3. The QuickTime 7 player will only be present if a QuickTime Pro key was present at the time of installation, or if specified as part of a custom install, or individually downloaded:

http://support.apple.com/kb/dl923

Snow Leopard update 10.6.4 included an update to 7.6.6 (if installed). You can install it from the above link even though it says for 10.6.3. It's the same version of QuickTime Player 7.6.6.

(Only QuickTime Player 7.6.3 or 7.6.6 can be updated to "Pro".)

A Mac OS X v10.6, OS X Lion, and OS X Mountain Lion-compatible version of QuickTime Player 7 is available for use with older media or with AppleScript-based workflows. QuickTime Player 7 can be used to playback formats such as QTVR, interactive QuickTime Movies, and MIDI files. Also, it supports QuickTime 7 Pro registration codes for access to QuickTime Pro functionality.

How to install Quicktime Player 7 on Snow Leopard, Lion and Mountain Lion when it is not already present:

http://support.apple.com/kb/HT3678?viewlocale=en_US&locale=en_US

Quicktime Player 7 for Snow Leopard OS 10.6 available here:

http://support.apple.com/kb/DL923

I can´t watch movietrailers on Itunes movietrailers. It tells me to download Quicktime but I already have Quicktime in Mac OS X? I can´t update Quicktime either?

How are you trying to watch the trailers—in a browser or a QT X/7 player app?

1. If using a browser, which one? Some no longer support the QT player plug-in as Safari still does.
2. If using a media player, which one and how are you recovering the URL or downloading the file?
3. If you have an Apple IOS device, have you tied viewing trailers on it using the iTunes specific app?