The Arduino Uno contains two microcontrollers.
The main ATmega328P and also a ATmega16U2 for usb-to-serial communication.
Both microcontrollers can be programmed with the 6-pin header. I hope you didn't try that.
It should be recognized by the computer. The driver is in the file that contains the Arduino software.
Do you use the newest 1.0.3 ?
The Arduino has be set properly: board, programmer (if you have one) and serial port.
You can use a programmer or the usb-serial connection to upload a sketch. But if you don't have a programmer, you can't upload using a programmer.
Try using the buttons to control the sketch and upload it.
But only after the device driver is valid. If that is not working, the Arduino Board could be defect.