mackrackit,
Thank you for guiding me in the right direction. I did some more research and found out that the internal USB regulator must be turned off. The capacitor at Vusb is not needed anymore and the internal USB transceiver and pull-up resistors can be used in the configuration I'm using. I just need to feed 3.3V at Vusb and Vdd.
So, I'm running my PIC18F4550 with Vdd=3.3V and the USB peripheral works! I was able to send and receive data from my computer to the PIC.
As for the GLCD backlight voltage, I have already ordered this chip and the required external components from mouser.com
http://www.onsemi.com/pub_link/Collateral/NCP5007-D.PDF
This chip is a backlight LED boost driver. The input voltage range is from 2.7 to 5.5 Volts, so it should work for my application.
Thank you all again for your help and ideas.
Robert
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