ho un esempio in vb che chima le api
codice:
Private Const TH32CS_SNAPPROCESS As Long = 2&
Private Const MAX_PATH As Long = 260

Private Type PROCESSENTRY32
dwSize As Long
cntUsage As Long
th32ProcessID As Long
th32DefaultHeapID As Long
th32ModuleID As Long
cntThreads As Long
th32ParentProcessID As Long
pcPriClassBase As Long
dwFlags As Long
szExeFile As String * MAX_PATH
End Type

Private Declare Sub CloseHandle Lib "Kernel32.dll" (ByVal hPass As Long)
Private Declare Function CreateToolhelpSnapshot Lib "Kernel32.dll" Alias "CreateToolhelp32Snapshot" (ByVal lFlags As Long, ByVal lProcessID As Long) As Long
Private Declare Function ProcessFirst Lib "Kernel32.dll" Alias "Process32First" (ByVal hSnapShot As Long, uProcess As PROCESSENTRY32) As Long
Private Declare Function ProcessNext Lib "Kernel32.dll" Alias "Process32Next" (ByVal hSnapShot As Long, uProcess As PROCESSENTRY32) As Long

Private Declare Function FindWindow Lib "User32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long

Private Declare Function PostMessage Lib "User32" Alias "PostMessageA" (ByVal Hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Private Declare Function IsWindow Lib "User32" (ByVal Hwnd As Long) As Long
Private Declare Function GetWindow Lib "User32" (ByVal Hwnd As Long, ByVal wCmd As Long) As Long
Private Declare Function GetWindowLong Lib "User" (ByVal Hwnd As Long, ByVal nIndex As Long) As Long
Const GW_OWNER = 4
Const GWL_STYLE = -16
Const WS_DISABLED = &H8000000
Const WS_CANCELMODE = &H1F
Const WM_CLOSE = &H10

Private Function ProcessoAttivo(NomeProcesso As String) As Boolean
Dim uProcess As PROCESSENTRY32
Dim continua As Long
Dim Verifica As String
Dim hSnapShot
hSnapShot = CreateToolhelpSnapshot(TH32CS_SNAPPROCESS, 0&)
If hSnapShot = 0 Then Exit Function
uProcess.dwSize = Len(uProcess)
continua = ProcessFirst(hSnapShot, uProcess)
ProcessoAttivo = False
Do While continua
    continua = ProcessNext(hSnapShot, uProcess)
    Verifica = uProcess.szExeFile
    If Trim(Verifica) <> "" Then
        If InStr(1, LCase(Left(Verifica, InStr(1, Verifica, Chr(0)) - 1)), LCase(NomeProcesso)) <> 0 Then ProcessoAttivo = True: Exit Function
    End If
Loop
Call CloseHandle(hSnapShot)

End Function


Public Sub tiraGiu(par)
Dim winHwnd As Long
winHwnd = FindWindow(vbNullString, CStr(par))
If winHwnd <> 0 Then
    PostMessage winHwnd, WS_CANCELMODE, 0, 0&
    PostMessage winHwnd, WM_CLOSE, 0, 0&
End If
end sub

If ProcessoAttivo("Nome Processo") = True Then
   tiraGiu "Nome Processo"
End If
ho solo questo, chon non usa un TerminateProcess, ma invia un msg di chuisura alla finenste
Per avere il processId forse lo trovi dentro alla struttura PROCESSENTRY32, quindi la varibile uProcess di ProcessoAttivo.
Con questo puoi usare il termitateProcess
Però non so come fai a distinguere ad esempio tra le diverse istanze di IE