Quicktime 7.1.6 unable to play

QuickTime can't open all files and many formats require third party software.
What is the file extension found in the email attachment?

I have a client who's been experiencing similar problems:

"Safari complains that it was unable to download a Veoh plug-in... Other browsers do nothing (OmniWeb, closely related to Safari) or crash (Firefox)."

On the other hand, those same Quicktime files work fine when he tries to open them up in Windows. Also, I've asked a number of my co-workers to test the movies on THEIR Macs (I don't have one myself), and it seems that my client is the only one experiencing this problem.

Anybody have an idea why this is happening? What kind of software/updates would he have to download in order to get Quicktime to work on his computer? Or is it a problem at my end, with either the videos themselves or the web site displaying the Quicktime videos? Any coding experts here?

By the way, my Quicktime files are all using the extension .mov
...if that's at all helpful

Please post a URL so we can see the page code.

Many WMP formats are encoded using codecs not supported by the Mac OS so you'll need a PC to view them.
If Flip4Mac component can't open the file via QuickTime then there's not much else you can do but ask the sender to encode using older settings.
It's not a QuickTime issue.