USB2 is about 40 times faster than USB1. How can you tell? Well it will be stated in your computer specifications - that's the easiest way of finding out.
Both USB types are compatible with each other but a USB2 device will only work at USB1 speed if plugged into a USB1 port (making it useless for high speed requirements such as video or DVD work). Likewise, a USB1 device still only works at USB1 speed whichever type port it is connected to.
You should be OK with a scanner in either type port.