Hmmm... try the in_mpg123 Winamp plugin. It's a MP3 plugin that supports replay-gain and gapless decoding.
in_mpg123 for Winamp ≥ v5.3in_mpg123 for Winamp < v5.3It looks like Shibatch started using 7-Zip compression, so you'll either need 7-Zip or WinRAR. To install it, just open the compressed file and navigate to the bin directory. Next, you'll have the options of normal or SSE2. Use normal if you have an AMD processor pre-Opteron or a Intel processor pre-Pentium 4. If you have a Pentium 4, Pentium M, Celeron, Celeron M, Core, Opteron, Sempron, Turion 64, or Athlon64, then you can (and should) use the SSE2 version. Just drop the in_!mpg123.dll file in your Winamp plugin directory. You'll also want to delete (or rename or archive) in_mp3.dll.
Unfortunately you'll loose the ID3 tag editing interface used by in_mp3. But you can supplant it by using foobar2000 to edit tags, or by installing install mp3infp.
You can read more about it
here.