The command "gksu nautilus" runs the normal file browser but in "root" mode. That means you can edit files in the file system that are normally off limits to you as a user. Beware, you could break something if you edit or delete something critical.Sorry, coldraven, but this has got me lost. I've never used gksu nautilus before, so when I typed it into Terminal, gave it my password, I was then faced with a Terminal line -"Initialising nautilus-gdu extension " and a window showing my home folder. So my next step is unknown to me.
It is probably better to use speartip's advice which will auto-update.
For your future information, if you had used nautilus and clicked on "File System" then "usr" then "bin" you would have found that the get_iplayer file lives in that folder. In geek speak you would have been in /usr/bin, where the leading forward slash means the root of the file system.
Tip: In /usr/bin are hundreds of files. To see get_player just start typing "get_" to jump to the the file.
As an experiment go to any folder in the nautilus file browser and then press Ctrl+L. You will see that the location bar changes to show the path as mentioned above. You can actually copy and paste a location there, hit Enter and that's where you will go.
Note: pressing Ctrl+L again should toggle the location bar style but no longer works in Ubuntu 12.10
Hope all is working now.