OK. First go to the folder /Library/QuickTime/ and make sure you have no DivX plugins plus any other weird QuickTime codecs.
Now go to System Preferences>QuickTime->Advance tab and make sure the Transport Setup is set to Automatic. Plus click on MIME Settings ... and make sure you have check marks in Stream & Video.
If one of these suggestions works, download the full 110MB 10.5.1 Update.
Mac Pro Dual 2.8 Quad (2nd gen), 14G Ram, Two DVD-RW Drives, OS X 10.8.3
2006 Mac Book Pro 2.16 (first Gen) OS X 10.7.4
2TB Time Capsule, 2 TB
32G iPhone 4S Black, iPad (3rd Gen) 32G Black