Iaprincessa is absolutely right! My solution isn't going to work for everyone, but we have two cars--mine is the official 'Dogmobile' and in spite of vacuuming, (the car and the dog) it's still got dog hair everywhere.
But, you can put a real dent in the hair problem, you just have to be vigilant. Pet supply stores sell 'hammocks' that sling over the back headrests of the front seats and attach to the rear seat head rests. Most (not all) the hair ends up in the hammock. The other advantage to these things is that the dog can't fall off the back seat and also can't 'visit' you in the front...
The next strategy is to get a handheld vacuum and vacuum the heck out of everything when you and your dog comes home. These things aren't as effective as canister vacs, but they get rid of more hair...
Next line of defense is to vacuum your dog. I have a Dyson canister vacuum; they sell an attachment that you use on the end of the flexible hose. It has two positions that you operate with your thumb: bristles extended to brush through his coat, and bristles retracted so the hair gets sucked up into the vacuum. I've heard that it fits on other vacuum cleaners, too. This not only combats the hair in the car, but it seriously reduces the fluff in the house and on our clothes.
Final step: Once a week, get out the shop-vac and use the crevice tool to get all the hair that is stuck on the seats, carpets, console, dashboard, steering wheel, gas pedal, inside the glove compartment... you get the idea!
As one final suggestion, when the hair gets unbearably bad in the car, I roll down the windows, open the sunroof, and get on the highway (no dog in car!) The hair gets dislodged, swirls around the car, then finally flies out the window. Other drivers must wonder, but hey, it works!