Trust me it's not hard for anyone who hasn't been dropped on their head a lot an an infant.
I couldn't find anything step-by-step on the web. If you want something detailed you may have to buy a book like "The Guitar Players Repair Guide" by Dan Erlewine. Here's some stuff I found at the Seymour Duncan site:
Is it hard to install a pickup?As a rule pickup installation is fairly simple but some guitars and switching layouts are more difficult than others. If you have basic soldering skills, a little mechanical aptitude and the ability to follow very simple color-coded diagrams you should find installing new pickups fairly easy and a lot of fun. Semi-hollow bodies, such as a Gibson 335 are more challenging and require a few special tricks to complete the job effectively. If you are inexperienced at installations, this type of guitar may be best left to a qualified, experienced repairperson.
What do I need to install a pickup? A basic 30 watt or 40 watt soldering kit usually contains all the tools needed to install a pickup, including the iron and solder, a small standard and Phillips (crosshead) screw driver, and a small pair or wire snips. A set of wire strippers or a single-sided razor blade is also helpful for stripping the insulation from the pickup leads. Also, some fine sandpaper to scuff the backs of the volume and tone potentiometers and some soldering flux to distribute the heat evenly on the potentiometer casings can also be very helpful. Soldering kits can be found at most electronics parts retailers.
More info here:
http://www.seymourduncan.com/website/support/faqdescr.shtml#installtools
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