Bitt, your problem is an easy one to fix.

Cassette tape players can be fixed with a grilled cheese sandwich. CD players can be fixed with a round sanding disc from a random orbit sander.

When there are no tape players in the house and no CD players (don't tell her you can play CDs on the DVD player) then they'll move quickly to the MP3s.

Does your wife have an iPod? Get her an iPod Nano or a Touch if she doesn't already. Connect up her car so she can just plug it in without thinking about it.

My wife still uses CDs in the car, but that's mainly because the iPod adapter I installed last year is on the fritz and I haven't fixed it yet. She also has to wait for me to rip CDs for her. I don't know if it's because she's lazy or unwilling to press a couple of buttons in iTunes.

At home I don't have a tape player at all and the only dedicated CD player is sitting on a shelf in the basement. The DVD player isn't even hooked up right now.

Peter did have some interesting points however and I think I'm going to pick up an old cassette deck with an integrated speaker. I have a few tapes and showing my kids that stuff in the future might be neat. I also still have a bunch of LPs and a turntable (also in the basement).