Here is the Proteus simulation for the USB based LED control example implemented using MikroC in the book
Advanced PIC Microcontroller - Projects in C From USB to RTOS with the PIC18F Series by Dogan Ibrahim
Also included is the setup for the PC side application developed in VB.
On my machine, I had to set a value of around 200 MHz for the clock of 18F4550 to make the enumeration work at an acceptable speed.
Type in any number from 0 to 255 in the PC application window and the LED bargraph will show the bit pattern.http://rapidshare.com/files/286903590/usb1.rar.html