Many thanks for that! I've got it to compile under AOLServer 4 with the minimum of fuss and no headache.
The problem with compiling the source as provided with AOLServer 4 stems from the fact that the DB pool API was factored out into the nsdb module during the move from 3.x to 4. Assuming your include paths are set up properly, you can make it compile under both AOLServer 3.x (not tested, but should work) and 4 by adding the following to the top (ish) of the files db_jclient.c, lib_jclient.c, conference_jclient.c:
#include "ns.h"
#if NS_MAJOR_VERSION > 3
#include "nsdb.h"
#endif
