http://www.riverstonenet.com/solutio..._desktop.shtml
A quote from this article
" According to research conducted by the Gigabit Ethernet Alliance (GEA), over 85% of enterprises use a Category 5 UTP copper infrastructure for desktop connectivity to the wiring closet. In addition, tests have shown that over 90% of the installed Category 5 wiring is fully compatible with Gigabit Ethernet. In particular, any Category 5 link currently carrying 100 Base-TX traffic at low error rates is also capable of carrying 1000 Base-T traffic. "
JP