Hi,
When the interrupt fires and the program jumps to myInt, the first thing you do is check the various interrupt request flags (INTCON.0 for INT0, INTCON3.0 for INT1 etc) to determine which one actually caused the interrupt and act accordingly.

Once you realise the limitations of ON INTERRUPT make sure you look into Darrels DT-INTS routines. Plenty of posts on that on the forum.

Can't help with the USB I'm afraid, too much voodoo for me ;-)

/Henrik.