Take the lameenc.dll file and extract (uncompress) it to a directory on you hard drive. The directory where you installed Audacity would be a good idea. This is probably C:\Program Files\Audacity or similar if you used the installer
Open Audacity and go to Edit > Preferences.
Go to the 'File Formats' tab.
In the bottom of the window there is a section tabled 'MP3 Export Setup'.
Click on the link tabled 'Find Library'
This will ask you if you want to locate the lame encoder. Click 'yes'.
In the dialogue box, go to the folder where you put the lame-enc.dll file earlier, and select it.
Click OK.
You should now be able to export files to the mp3 format. Walter.
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It don't mean a thing, if it ain't got that swing!!!