Bicycle Mechanics - Bike didn't shift into all gears

I was trying to fix my sister's bike, which could only switch between 4 gears in the rear. I read in Zinn and the Art of Mountain Bike Maintenance to tighten the rear shifter cable, which I did. This only changed the 4 gears between which I could shift. I ended up taking it to my LBS, but he didn't want to share his secrets. How did he fix it?

http://sheldonbrown.com/derailer-adjustment.html
http://www.parktool.com/repair/byregion.asp?catid=53

Probably at some point, somebody fiddled with the derailleur's limit screws. Once those have been properly set they never need readjustment. Twisting the limit screws, if you don't know what you are doing, almost always makes whatever problem you are having worse.

Reset the limit screws with the cable detached, then reset the cable tension. Make sure the shifter is in the highest gear, assuming a high normal derailer.

I have run into a couple of shifting problems with Campy 10 speed rear derailleurs. One time on a bike that I built from scratch after buying a frame and building it up. Next a friend had his shifters rebuilt and it kept skipping gears in the middle of the cassette.

Both cases were based upon the limit screws. I found that if you open the screws up way beyond necessity, start from the outside gear, adjust the cables, then set the limit screws only at the end of the process, I was able to get back in sync. What is scary, you can hit the highest gear and the lowest gear, but it seems to skip in the middle. The chain dances up and down between a couple of gears and it seems you can't time them all. After opening up the limit screws, adjusting the cable, the resetting the screws, we eliminated any problems. One time, it was a new derailleur setup, another a five year old rebuilt set of shifters. Same result.

What I learned was to let the shifter control the chainwork through it's detents, then set the limit screws to prevent overshifting.

Thanks for all the advice. I did read Sheldon Brown's guide as well as the Zinn book. If I run into the problem again, I'll knuckle down and figure it out myself, instead of taking it in to the shop. Of course, if my sister's bike had some nice friction thumb shifters, this would all be unnecessary :-)