That’s no longer true, thanks to the ever-spreading MP3 revolution. Once the province of desktop PCs and portable music players, MP3 technology is making its way into car-stereo products like the Kenwood Music Keg. The device consists of three parts: a 10-gigabyte removable hard drive, a USB docking cradle that connects to your PC and the in-car or trunk-mounted Music Keg. To copy music from your PC, you simply place the hard disk in the cradle and transfer your songs and playlists, then take the hard drive over to your vehicle and pop it into the Music Keg. At $900, the Music Keg is a lot more expensive than burning your own CDs. But it sounds great, down to the mournful strings on the Beatles’ “Eleanor Rigby.” And with 2,500 songs at your disposal, you’ll never have to fumble with a stack of CDs again.