You could try using a crude method of timing a large file transfer to/from the usb drive if that is what your using yours for.
The specs below should give a useful guideline to base your times.
Q1: How fast is USB?
A1: High speed USB products have a design data rate of 480 Mbits/s. Full speed USB devices(2.0) signal at 12Mbytes/s, while low speed devices(1.1) use a 1.5Mbytes/s subchannel
Or you could check your device manager and see what chipset is being used , if it is either a Compaq, Hewlett-Packard, Intel, Lucent, Microsoft, NEC or Philips then It's almost certain your USB 2.0.