#define TTN_FIRST (-520)
and similarly many other notification messages are
defined as negative numbers; since they are stored in
the "UINT code" memeber of struct NMHDR, I think
they all should be ((UINT)-520)
I think PSDK defines them like this (tested with MSVC5,
UINT x = -1; warns, UINT x = TTN_SHOW; does not).