<p>I need help converting WAV files to MP3 format in VB6. I did already find <a href="http://www.codeproject.com/KB/audio-video/MP3Compressor/MP3Compressor.zip" rel="nofollow noreferrer">source code in C#</a>, but I can't use that</p>

AFAIK, MP3 compression is under a patent, you can do that legally only by buying a license.
Or, like many other softwares, use the Lame DLL without distributing it but asking to download it in a site not under the same laws...
Somehow, that's how Opera does with GPL software: they don't provide spelling correction out of the box but they instruct to download and install aspell...
Note you can use free alternatives, like Ogg Vobis, it depends on your purpose.