Since my Windows Media Player 10 doesn't have MP3-burning capabilities, all MP3s are converted into WMA format. The CD players I have will play the WMA format that I've burned onto my CD-Rs. My only problem is that the CD player in the car won't always play the CD-Rs. I get around that problem by playing them in my portable CD player and using the cassette adaptor to play it through the car's tape player, since my portable CD player will read CD-Rs, even if they're burned in WMA format.