As anyone who has ever successfully monkeyed with a computer will tell you, the minute you put a family member's Mac to rights, you become the IT department for your entire clan (and every single "close personal friend of the family"). Take this message from my sister, for example:
Can I call you tomorrow night and have you walk through the setup of my AirPort Express? I started to do it but then it wanted me to reconfigure my network and I was afraid I was going to hose the whole thing. Wasn't that good of me to wait??? Right now it is plugged into the kitchen and is blinking yellow. I mostly want to use it to extend the power of my AirPort to other parts of the house.
I might also mention that when members of your family (and their friends) ask for help, it's only after they've committed some unforgivable sin -- cleaned their monitor with turpentine, surrounded their CPU with pillows to make it quieter (and, thus, blocked vents necessary to cool it), or thrown out a host of files for which they knew not the purpose.
In this case, my sister purchased an AirPort Express without bothering to ask me if it would do what she wanted with her current wireless setup. Had she, I would have responded:
She has a second-generation white AirPort Base Station and the AirPort Express can extend the range of AirPort Extreme Base Stations and other AirPort Expresses only.
"If you need greater range," I might have said, if given the opportunity, "you might look at one of the AirPort Base Station antenna upgrades."
Ah well, at least I can tell her that the blinking yellow light indicates that the AirPort Express can't establish an IP connection -- not surprising given that she didn't allow it to join her network.