At best, a PIC can do "Full Speed" USB. Which is compatible with USB 1.1.
So the old laptop should be fine.
also, incidently, what is that config flag, and where do i read about them?
To find out what they do... look in section 25.1 of the datasheet. Under "Special Features of the CPU" / "Configuration Bits".

To find out what to call them in your program, look at the bottom of the P18F4550.INC file in the same folder as MPASM.