Hello,
Browsing by cd to the planeshift directory is good.
What I don't understand is why you need to be super user for the install. Just as a note, it also should work as normal user.
The question is, what you typed exactly as chmod command. If you didn't set the file as 'executable' with this command, you will get an error like you described, so I think there is the error.
-> Example for chmod command: chmod 755 ./Planeshift....bin
This sets the ./Planeshift....bin to executable for the current user.
Sen
*edit* Typo, as always -.-