Hi Mohamed, you have too many solutions for this issue, some of they are:
1- Use a FTDI chip, I don't remember the part numbers but is something like FT232. Search google.
2- Use another PIC, as the PIC18F4550. This pic is similar in pinout to 877A, but richer in features. Also there is a USB stack from Microchip, FREE, and also from many others, just google it.
3- There are too many solutions, search in google for PIC with USB interface or other chip options.
I hope this help you. Best regards. Yosmany325