Cat5 doesn't work well with gigabit Ethernet. Found it out the hard way: Couldn't get the Internet connection with a Gigabit NIC connected to a Cable Modem which apparently had a Gb jack too. The same cable had worked perfectly with the 100 Mbps built-in NIC of the old computer, and continued working at a replug. Took quite a while to figure out why the new computer wouldn't connect...
Generally speaking you can use the previous generation of cable for the next generation of speed if you shorten the maximum length by an order of 10 (assuming properly wired). So a Cat 5 good for 100 meters of 100Mb should run 1Gb if you keep it to 10 meters or less. 10 meters is still a pretty long cable. Obviously this is only for home adhoc use, not in-wall or in business.
Personally I bought a spool of 1000 feet of Cat 5 for around $40 in 1996 and I make my own cables for home use as I need them, and if I get the ends on right, never have problems carrying gigabit speeds. In fact, once made and tested, they are more reliable than random patch cables found with power strips, cable modems, etc.
