DON'T INSTALL When you go to a p0rn site and it says it, that is a TROJAN! Read about it at this MacWorld article.
To play most every video file (except Windows DRM files) use the only two QuickTime Player will need, Flip4Mac and Perian. If you need any other Quicktime plugin, reject it! With these two Quicktime plugin will be the only one you will need on 10.5 Mac.