Yep, you got that last one right. There is nothing you can do to spot true from false other than actually dlding a small bit of the file then Prview-playing it in LW's player (that's why it's there for). That way you'll know if what you are dlding is trully what you want. Just remember to select (in the Finder) an .avi file and press Cmd-I (the Cmd key is the one with the apple on it) and then select Open with and choose VLC, then click the "Change for all" button. That way, when you'll press Launch on a dlding .avi file, then it will try to play in VLC, not Quicktime.
Also, if you spot a badly named file and the one that is serving it has enabled chat, then open up a chat window with the user and tell him about it. If he is doing it on purpose, feel free to badmouth him and to generally insult him (I know that I wouldn't mind. Really).

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-