I ran into a hurdle. I can't install QT 7 because I already have QT X--and the installer said to use the software update function to stay current.
You are probably trying to install the Leopard version of the QT 7 Player app on a Snow Leopard system. Instead, install the special Snow Leopard version of the QT 7 Payer app. (Use the installer on your Snow Leopard installation disk for Snow Leopard OS earlier than vX.6.3 or the QT Player 7.6.6 for Snow Leopard vX.6.3 and later.)
Which is more current--7 or X?
QT 7 is the product of 20 years of development. As such, it has more features, can be upgraded as an editing utility ("Pro" keyed for $29.99), and has better compatibility with older compression formats. The QT X player is based on new technology but is still in its infancy as far as development is concerned. Since both apps can be installed and used simultaneously under Snow Leopard, most serious users keep both installed and use whichever best suits their needs at any given time. (Note: The Snow Leopard version of QT 7 is installed in the "Applications/Utilities" folder and should be kept there if you want it to be recognized/updated automatically.)