I am going through the same thing at the moment.... You can test your speed sensors pretty easily. Jack the car up, disconnect ABS harness plug from the ABS module. Using a volt/ohm meter measure the resistance between each of the wheel sensor pins.... should be about 1K ohm. Now measure the A/C voltage between the pins while someone spins the wheel, should get something in the neighborhood of 100mv. If you have an oscilloscope use that, it should show the A/C wave form as it spins.
You can also measure at the wheel sensors but it is better to just measure it at the pins since it will detect a wiring problem in the harness (e.g. wire break). Of course, if you find a problem, take the tire off and measure the sensor directly to rule out a harness problem.
I just broke down and bought a equus 3160 scanner so I can read/reset the ABS codes ($200).... Part of the problem is if you do find a bad sensor and replace the bearing, it will take 100 ignition cycles for the ABS computer to turn off the light (according to the bosch manual anyways).
