I have the same problem, and after several trial and error, I find a solution that is most suitable for me, and I would like to share with you guys.
If you search for "unicode" in Windows2000 Help, you will find a article telling you how to display non-Unicode programs in their native language.
For the following, "old files" means files with Chinese name created/re-named under Windows9x with Njstar Communicator (or the like). "new files" means files with Chinese name created/re-named under Windows2000 with either Njstar or Windows built-in MIME.
If you install Windows2000 English version, you have English as your default Language. Then, you are able to play the old files; you just can't see the Chinese words. However, you cannot play the new files.
If you want to play new files, then you need to set your "Language setting for system" to Chinese. After restarting, winamp can then play the new files. However, at the same time, you cannot play the old files.
I think the best way is to convert (retype) all your old files under Windows2000 with Chinese as your default "Language setting for the system". That way you can play files with Chinese right away, and when winamp eventually support unicode, we can switch back to English as the default "Language setting for the system".