EMP is not as effective as everyone seems to think. For a start, the power requirements to obtain a decent incident voltage on an unhardened target at a decent range are massive. With current technology, it would certainly not be a portable weapon. Secondly, not everything electronic is susceptible. Things like spark plugs already deal with a fair amount of voltage compared to, say, a laptop CPU, so you'd need a powerful EMP to break it. You're more likely to damage computerised components such as the engine management system. Of course, something like a PC would be relatively easy to damage if it were out in the open. Which brings us to the last constraint: vulnerability. Your average building would provide an EM attenuation in the order of 30 dB. That's a lot. That's just with bricks and curtains. So you may be pointing a powerful EMP at a building, but the incident voltage that manifests on the target electronics would be comparatively weak.
When technology has improved for power supply units, so that you can store huge quantities of energy in a small box and release it quickly, then you might be able to make a decent EMP weapon. I found a website a while ago with instructions on how to make a small one which could disrupt an active mobile phone from a few feet away. I don't remember how to get there though.
