I'd just second Wendy's recommendation of iRivers. I don't have one with nearly so large a hard drive (too much money!), but I've had absolutely no trouble with my smaller model. And mine runs on regular (or rechargeable) AA batteries, which means its always easy to pick up new ones if I run out.
As for adapting it to work in your car, unless you can plug it into an auxiliary slot as Wendy says, there isn't any way to run your player through a CD stereo system. You can't plug it into the CD player itself the way you would a tape player. THe only option I can think of is to get one of those small radio transmitters. You plug them into your mp3 player and it transmits the sound on a radio frequency. Then you just tune your car radio to that frequency. I don't have any experience with these, though, so I can't tell you how well they work.
Kaylle
