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In Nero, are you burning the disc as a data or Audio disc?
If you burn them as an Audio CD, you'll not see MP3 or wave files in My Computer, as the songs are not actually stored as files on the CD, but as audio tracks. Most audio playback software, including Windows Media player, Winamp and iTunes will play the tracks directly on the CD.
However, if you burn the disc as a data CD, you will see the wave or MP3 files when you browse the disc in My Computer. If you only plan playing your CD in your PC / laptop, it's best to write MP3s as a data disc, as you can fit a lot more MP3s on a CD than audio tracks. However, if you burn a CD as a data CD with MP3s or wave files, this CD will not play on standalone CD players (e.g. Hi-Fi system), apart from those that play MP3 files.