USB complete by Jan Axelson is a very good book which covers both, PC and Microcontroller. The PC code is described in the book in VB and C#.
The Author also has downloads to example code on her website, which is where I began, If you dont mind coding in C# **broken link removed**
For the PIC side of the design look at the the examples which came with your compiler. I use the PCW compiler which has some good human interface device examples.
You need to understand the USB descriptor tables, there are some good online resources too. Try "usb in a nutshell" or "usb made simple"