I'm not even sure why I'm correcting you on this -- I know it's an aggravating habit, but... I don't know, I'm a stickler for accuracy, what can I say. Vidalia isn't the client. "tor" is the executable that does all the Tor stuff. It also opens a local connection via one of several methods (depending on your operating system) for external programs to connect to it and issue commands and whatnot. Vidalia is a graphical program that does exactly that -- provide some buttons that map to appropriate commands being sent to the "tor" program. Technically they're independent of each other; tor works just fine if you configure it from a startup text file. Vidalia is for the mouse-centric among us :)