1. Find a .flv file that you want to play.
2. Right click the file and select "Get Info" (you can Command + Click if you are still using a 1 button mouse or press Command + I or select Edit > Get Info from the menu bar
3. In the section labeled "Open with:" use the drop down menu to choose "Other"
4. Using the resulting navigation window, find the VLC player and choose it.
5. Back in the Get Info window, under the statement "Use this application to open all documents like this one", click the marked "Change All"
6. VLC should now be the default player for all files with the extension .flv
You may be interested to know that there are 14 forums on CNET that deal with Mac related questions.
Here is a link to one of them, you can reach all the others from that page by using the sidebar.
Let us know how you get on with the above instructions
I can't figure out how to do it.