Cat 5 vs. Cat 5e

Cat 5 and 5e are identical in every way except for two things:

1. At the center of a 5e cable is a plastic line that separates the four pairs. This helps to reduce crosstalk. Cat 5 does not have this plastic line.
2. Each wire in a 5e cable has thicker insulation, again to reduce crosstalk.

Apparently, the pairs are much more suseptible to crosstalk at 1GB/s then 100mb/s.

Other than the external labeling, you would have to cut the cable open and look for the centered plastic line to tell the difference.

If the cable isn't branded "CAT-5E", it isn't. Took up the specs for the cable you have installed on the manufacturer's website just to be sure.

Also, just because the cable is a certain rating doesn't mean that your wiring system is. You also have to evaluate your wall jacks, patch panels, termination techniques, etc. "Everything" has to be installed to the same standard.