Где найти Описание функций из Winmm.dll? http://msdn.microsoft.com не открывается.

Вот ссылка на первую ф-цию из этой библиотеки CloseDriver()
http://msdn.microsoft.com/en-us/library/dd797785(VS.85).asp
Я для таких целей использую программу depends.exe.Она показывает список ф-ций и их сигнатуры в dll.Далее, если это стандартные API,то инфу по ним можно искать в MSDN.

Вот часть функций, определенных в winmm.dll. Если интересуют подробности, пишите в личку.

ULONGLONG __stdcall VerSetConditionMask(ULONGLONG ConditionMask, DWORD TypeMask, BYTE Condition)
int __stdcall GetSystemMetrics(int nIndex)
BOOL __stdcall SystemParametersInfoW(UINT uiAction, UINT uiParam, PVOID pvParam, UINT fWinIni)
LPSTR __stdcall CharUpperA(LPSTR lpsz)
HICON __stdcall LoadIconA(HINSTANCE hInstance, LPCSTR lpIconName)
ATOM __stdcall RegisterClassA(const WNDCLASSA *lpWndClass)
HWND __stdcall CreateWindowExA(DWORD dwExStyle, LPCSTR lpClassName, LPCSTR lpWindowName, DWORD dwStyle, int X, int Y, int nWidth, int nHeight, HWND hWndParent, HMENU hMenu, HINSTANCE hInstance, LPVOID lpParam)
BOOL __stdcall GetMessageA(LPMSG lpMsg, HWND hWnd, UINT wMsgFilterMin, UINT wMsgFilterMax)
LRESULT __stdcall DispatchMessageA(const MSG *lpMsg)
BOOL __stdcall DestroyWindow(HWND hWnd)
LRESULT __stdcall DefWindowProcA(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam)
BOOL __stdcall PostThreadMessageA(DWORD idThread, UINT Msg, WPARAM wParam, LPARAM lParam)
BOOL __stdcall PeekMessageA(LPMSG lpMsg, HWND hWnd, UINT wMsgFilterMin, UINT wMsgFilterMax, UINT wRemoveMsg)
BOOL __stdcall UnregisterClassA(LPCSTR lpClassName, HINSTANCE hInstance)
BOOL __stdcall PeekMessageW(LPMSG lpMsg, HWND hWnd, UINT wMsgFilterMin, UINT wMsgFilterMax, UINT wRemoveMsg)
int __stdcall MessageBoxW(HWND hWnd, LPCWSTR lpText, LPCWSTR lpCaption, UINT uType)
SHORT __stdcall GetAsyncKeyState(int vKey)
int __stdcall LoadStringA(HINSTANCE hInstance, UINT uID, LPSTR lpBuffer, int cchBufferMax)
LRESULT __stdcall SendMessageA(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam)
DWORD __stdcall CharLowerBuffA(LPSTR lpsz, DWORD cchLength)
BOOL __stdcall PostMessageA(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam)
UINT_PTR __stdcall SetTimer(HWND hWnd, UINT_PTR nIDEvent, UINT uElapse, TIMERPROC lpTimerFunc)
int __stdcall LoadStringW(HINSTANCE hInstance, UINT uID, LPWSTR lpBuffer, int cchBufferMax)
BOOL __stdcall PostMessageW(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam)
BOOL __stdcall KillTimer(HWND hWnd, UINT_PTR uIDEvent)
UINT __stdcall RegisterWindowMessageW(LPCWSTR lpString)
BOOL __stdcall IsWindow(HWND hWnd)
int __stdcall GetObjectW(HANDLE h, int c, LPVOID pv)
int __stdcall GetBkMode(HDC hdc)
DWORD __stdcall WaitForSingleObject(HANDLE hHandle, DWORD dwMilliseconds)
. .
int __stdcall midiOutGetIdFromInstrument(LPCWSTR Str, int)
int __stdcall midiOutSetPersistentPreferredId(UINT_PTR uDeviceID, int)
int __stdcall midiOutSendPreferredMessage(DWORD_PTR dw1)
int __stdcall s_gfxLogoff()
int __stdcall s_winmmAdvisePreferredDeviceChange()

__declspec(dllimport) __stdcall NtQueryVirtualMemory(x, x, x, x, x, x)
__declspec(dllimport) __stdcall RtlUnwind(x, x, x, x)
__declspec(dllimport) __stdcall RtlDeleteResource(x)
__declspec(dllimport) __stdcall RtlInitializeResource(x)
__declspec(dllimport) __stdcall NtCreateEvent(x, x, x, x, x)
__declspec(dllimport) __stdcall NtWaitForMultipleObjects(x, x, x, x, x)
__declspec(dllimport) __stdcall NtCreateTimer(x, x, x, x)
__declspec(dllimport) __stdcall NtSetTimer(x, x, x, x, x, x, x)
. .
__declspec(dllimport) __stdcall NtSetValueKey(x, x, x, x, x, x)
__declspec(dllimport) __stdcall RtlOpenCurrentUser(x, x)
__declspec(dllimport) __stdcall NtQueryValueKey(x, x, x, x, x, x)
__declspec(dllimport) __stdcall RtlInitUnicodeString(x, x)
__declspec(dllimport) __stdcall NtOpenKey(x, x, x)
__declspec(dllimport) __stdcall NtClose(x)
__declspec(dllimport) __stdcall GetWinStationInfo(x)