Read this posting:

http://www.8052.com/forum/read.phtml?id=55662

And then look at this web page:

http://www.cygnal.com/products/CP2101.htm

The CP2101 is a couple USD ($) chip that will connect to your microcontroller UART port directly. Then you install the Cygnal supplied driver the Windows PC which provides a VCP (virtual comm port) interface. WHen the driver is configured properly then an application in the PC written in a language of your choice can open the VCP just like a normal COMM port and send and receive data via USB to the microcontroller. It couldn't be easier. You can get the eval kit for the CP2101 from Cygnal for $49 USD.

Michael Karas