So what kind of output.
http://mbed.org/handbook/Terminals
If your only trying to display a variable or receive some imput and "do stuff" You could go the old school route and use a serial interface and Hyperterminal (or something thats not so buggy or for your specific OS)
Basically you use one set of serial pins and put a serial port on the breadboard and then connect using the same settings in hyperterminal.
http://mbed.org/handbook/SerialPC
Its my first day reading into the capabilities of this thing, but I remember reading something about it having a usb to serial , I am just not for sure it was this board (Ive read a whole lot today). This option is a bit more complex as it uses USB but usually it is quite easy. (This is the equivelent of say a max232 only your building the interface, or if you use a library at very least have access to the interface) Same exact outcome as above only much more convieant for laptops and new pcs that dont have serial ports. In Hyperterminal it works basically the same as above with acception the settings are much less imparative (they are set in software).
http://mbed.org/cookbook/Text-LCD
A better way to do the above (print some variable) is to use the 16x2 character display library. These displays are very simple to use with a library and dont require too much to set up. They are also very affordable , say 13 $ from adafruit just to name something off the top of my head.
how can I use the pc to act as display for mbed derived output ?? tnx all........