PoE is somthing fairly common in many business/office spaces. For example, many wireless access points in office buildings and universities use the technology so they don't have to run a power receptacle to wireless access points. For this instructable though, we're going to use PoE in a residential setting. Even the big router companies are starting to sell these adaptors to consumers like this Linksys WAPPOE12. But I think it costs way too much and is kinda bulky. If you're into the DIY bulky thing though/have a need for an external PoE injector, you could try this option.
Applications for this instructable are up to your imagination. You might be relocating your wireless router to the centre of a house for better reception even though the cable modem installer might have put the cable modem say in the basement/some other inconvenient spot. Another useful application might just be to make an all weather-sealed outdoor access point with the famous WRT54G router inside it.
In my case, I will be using a 5 year-old WIRED router that I had lying around. Have no fear though, the points where we will be soldering are identical on every router/switch that you can get today. I should note that we're using cat5 here. If all you have is cat6, you can still go ahead and use that. But I should note, if you're connecting to a gigabit ethernet device, this instructable won't work. Luckilly, cable modems don't work at GigE speeds and I doubt the WAN port on your router supports GigE.
To begin we'll need some basic things:
1. A router
2. A length of cat5 cable (length depending on your location...mine was 10 ft.)
3. RJ-45 connector ends (...ok 8P8C for you technical people)
4. RJ-45 cable booties
5. A wall wart (power supply brick)
6. Some heat shrink tubing (I just used some random scraps I had lying around)
7. Your trusty soldering iron and some solder