JNI? I found some code in VB which clears the recycle bin
programmatically... but those are quite old, uses undocumented
features, and requires ActiveDesktop to be installed.

But even if those works, you still need to handle the new security in
Vista. Deleting items with some attributes require the program to
elevate.

 See also:

http://groups.msn.com/windowsscript/wshgeneralquestions.msnw?row=16&viewtype=2

 Even using wsh, this is difficult, because the actual verb
 ("&Papierkorb leeren", "&Delete") is localized and even under
 Windows 98 it might enforce user confirmation.

If you are running Vista, could you not put a *nix shell like Interix on
it and run your Java programs on that layer.  From there, it should be
easy to execute a ksh command like "rm -f /dev/fs/C/..../recyclebin"