The files are located in /System/Library/CoreServices/Springboard.app.
And, I feel compelled to add this caution: Please be very careful while you are mucking about in the "real" files of the iPad. When I first tried to remove this icon, I went into the file system and changed the icons. I messed up my iPad (an iPad1 at the time) and had to restore/re-jail break. That's why i decided to go the Winterboard theming route. Just so's you're aware...
Marilyn