Sometimes you can
find utilities that will convert between two formats that use
lossy compression but the results will probably be less than impressive.
When a tune is ripped into a lossy format it uses an algorithym to remove parts of the file that the creators of the format feel your ear will not miss. Since every format has different algorithym(s), different information will be discarded by each format in compressing a given tune.
When you try to convert from one lossy format to another it is almost a certainty that the original ripping will have discarded some of what the new format thinks it needs to do its job. To make matters worse, the new formatting will also discard some of what the original ripper thought was important for you to hear.
The result is that a
lossy to lossy conversion can never sound as good as
either one of the two formats.
The only way to change a tune's format without shooting yourself in the foot is if you have retained either the full sized CDA, WAV or RAW files and reformat from those. I archive audio in the open source FLAC format which will often reduce the size of the file to less than half the size of the originals. Because it is a
lossless format I can re-inflate the FLAC files back to
bit for bit copies of the originals with all of the information intact -- and
then convert them to any format I need.
If you only have the tunes in a lossy format you would be better off trying to find a
player that can handle the format on Win boxes.
This might be what you're looking for.
Here's more.
If you do convert lossy to lossy be sure to archive your originals.
EDIT: Added 2nd URL