Remember all the advice you got five years ago when you were shopping for home theater equipment? If you're not doing the work yourself, find somebody reputable, and don't be a cheapskate. Same goes when you're looking to install an iPod adapter or any other technology devices permanently in your car. Whether it's a DVD player in back, a new audio system in front, an alarm, a backup camera, or a hidden-wiring radar detector, the price should not be the first thing on your mind.

Over the past few years, I've installed, or had installed, in-car DVD players, satellite radio, an in-dash radio/CD, an iPod adapter, a Bluetooth adapter, extra power to the middle seats of a van, and some hidden wiring, and here's what I've found. None of this should be a revelation.

Installations mean squeaks and rattles. No matter how careful the installer, each panel removed and replaced and each screw undone and redone is unlikely to fit better or squeak less than before. One exception: AV gear installed in Yugos, Fiats, and British cars older than American Idol contestants, because you can only improve the original factory fit and finish. So if you're considering putting a DVD player in back, think about whether you're also going to need an additional power line to run your Xbox 360 (150-plus watts). If so, take care of all three at once (yes, three): 1. the DVD player, 2. extra power, and 3. audio/video inputs through the ceiling and side pillars to the floor, so you don't have cables dangling in the driver's rear view. A good installer would remind you of that. You'd think of it yourself, eventually.

Keep it short or keep it digital. Right now I'm trying to diagnose a horrible hum in my iPod adapter. An analog signal cable runs from the console to the trunk (where the CD changer input is located), and somewhere along the way, it's running parallel to a power line. If you have the choice, short runs are good, and digital signals are better than analog.

Is that how you'll really use it? I spent an hour figuring out the best place for a console-mount display panel. I checked my sightlines as well as my wife's. When the glue was dry on the display mount and I went for a test drive—uh, oh. The sightlines were perfectly established with the transmission in Park, not 3 inches farther back in Drive. Make sure your add-on doesn't get in the way of your swing-outcupholders, where you set the cellphone, where your purse goes, where it doesn't get in the of the handbrake.

Get the best techs possible on your side. "AM/FM/CD: $99, installed!" may be one of life's big dissatisfactions. Not to knock the national chain merchants, but the work they do is inconsistent. When you're buying a brand-name product, get a list of factory-authorized installers, and start there. Better yet, find out if the vendor has Platinum or Select dealers (the term varies) and look them up. Best of all, e-mail or call the electronics company and ask who it would recommend. Another possibility: Your car dealer probably jobs out unusual installations to a regional service center. Find out who it is and see whether it does work for individuals, too.

Hard-wire your satellite console. Once you've played with your new dash-mount satellite receiver for a week and decided life is not worth living without Sirius or XM (take your pick), spend $50 or $75 to have a technician hide all the wires. You can do a good job, but the tech can do a better job.

Check with Crutchfield. Lots of places will help you with a DIY installation. Some are cheaper, but none are more helpful than Crutchfield . For higher-end or more esoteric tech goodies for your car, also check out Auto Toys. No matter where you buy, it's a good reference tool.

Get the best audio-in quality. Try to use these audio connections, listed from best to scratchiest: direct line-in (often through a CD connector adapter), a hard-wired FM antenna modulator, a cassette adapter, a good wireless FM modulator ($25-plus, roughly), or a cheap FM modulator ($10 to $20).

Line-in is good, radio display is better. You can always bring in audio. But with iPods and satellite radio, sometimes you can also get artist and song information to show up on your radio display and control the device from the radio controls. Replacement radios may have iPod jacks and jacks for XM or Sirius (occasionally they have both). If you're working with an existing car radio, check out black boxes from Soundgate, Blitzsafe, Pacific Accessory Corp., and Precision Interface Electronics that adapt existing car radios.

Replace the radio. You're probably not wedded to your car radio. It may be cheaper to buy a new radio/CD player with an iPod connector and a satellite radio connector (or satellite built in) for less than the cost of add-on iPod and satellite adapters. Just be prepared for tinier buttons: The replacement-radio mantra is "big displays, small buttons."

One last word: Before you dive too deeply into AV technology, make sure you're doing it because you love the entertainment it provides. Tech gadgets like these won't do much for your car's resale value.