In the terminal, go to the directory where the Chimera installer you downloaded is.  Type "ls -l".  You should see a list of the files in the directory.  One of them (the installer) should be something like:

-rwxr-xr-x   1 chimera  staff    103907447 Jun  5 00:36 chimera-alpha-linux.exe

This would be if you had downloaded today's daily build.  If you had gotten the production release, the name would be chimera-1.2470-linux.exe instead of chimera-alpha-linux.exe.  The big number in the middle of the line is the file size.  Make sure it's the same as the size listed on the download page.  The string of letters on the left is the "permissions" for the file.  The last letter needs to be 'x' for it to be executable.  If it's not, type "chmod +x <name of the installer file>", then do "ls -l" again and check that it's executable.  Now type "./<name of the installer file>".  The installation should either start up or you get some kind of error message.  If you get an error, let me know what it is.

--Eric