Ok.. I found this: **broken link removed**
If you really want to go with USB, then you need to find out how to setup your PIC as HID device. I hope microchip has some examples (code) for HID devices.
This is maybe the easiest way to get USB communication working.
The drivers I linked are not free.. you can search for free HID drivers for matlab or write your own drivers.. But, if you can afford Matlab then 69 euros for the drivers probably are not a problem.