iTunes requires QuickTime 7.5.5 or later. For more information on upgrading your computer, visit http://www.apple.com/quicktime

I have a mid-2008 20" iMac running OS X 10.5.8, too. I am getting the same exact error. Yesterday I replaced the stock WD 500GB hard drive with a new WD 1TB hard drive. I, of course, loaded the OS on the drive, and everything seemed to be working perfectly. Before opening iTunes, I ran system update to get the OS X 10.5.8 and iTunes 10.5.1. This morning, after the update, I tried opening iTunes, and I received this error. I have Quicktime 7.7 installed. I have tried uninstalling and reinstalling both iTunes and Quicktime. No luck. Help?

Problem solved- at least for me. What I did was uninstall iTunes. Then I downloaded and installed iTunes 8.2 at oldapps.com. This version of iTunes worked fine. I imported all my music, which I had no problem doing. It all played fine. I then clicked on "iTunes Store." The iTunes store told me I had to update iTunes, so I downloaded it from Apple. It replaced the old version of iTunes, and 10.5.1 now works. I don't know what the problem was, but it seems to all be "fixed."

plssss help me i installed itunes 10.6, but when i try to open it says: ITunes requires quick time 7.5.5 , i checked on software update but there is not quick time plsss help meee !

Oldapps.com no longer hosts the old versions of iTunes for the Mac, only for Windows. We're stuck without working iTunes still as a result.

Hey Apple! If you set it up so your software encourages us to download new versions that won't work, at least keep legacy versions available. Thanks!

Apple does host iTunes 8.2.1 for G3 and G4 users. It's here: http://support.apple.com/kb/DL857. See the "Download" button in the upper-right corner of that page.

See this for your solution: Older media files may require iTunes to reopen in 32-bit mode, http://support.apple.com/kb/TS3771

I had the same problem after restoring my system from time machine, I uninstalled QuickTime and downloaded the new version, which is 7.7, and iTunes then worked.

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I had this same problem but then I went here:

http://support.apple.com/kb/DL27

And downloaded quicktime and the problem was solved, but if you don't have leopard you may need to look somewhere else; try searching for "quicktime 7.5.5 for (insert version - ex. tiger)"

The only problem I faced was when I opened iTunes it said I need quicktime 7.6 to watch video, but it works for music now so I'm leaving it