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There are some applications you can use as alternatives:

Applications:
Mac Blu-Ray Player - Plays pretty much any video file. Including Blu-Ray DVDs and files. Costs like $50 or something, but you can download it for free and it will still let you play videos. It will just ask you over and over to buy the full version.
VLC - Plays everything including music and videos. Free.


Components for quicktime (pretty much just perian alternatives):
http://www.xiph.org/quicktime/ - Free
Flip 4 Mac - Free



*Also, as the other person said; download the latest version and keep it for as long as you can.
 
Be sure to download the latest version and store it, in case you want to install it on other Macs later. (for as long as it works)
 
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