Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByRef lParam As Any) As Long

Private Type TVITEM
    mask As Long
    hItem As Long
    state As Long
    stateMask As Long
    pszText As String
    cchTextMax As Long
    iImage As Long
    iSelectedImage As Long
    cChildren As Long
    lParam As Long
End Type
Private Const TVIF_STATE As Long = &H8
Private Const TVIF_HANDLE As Long = &H10
Private Const TVIS_CHECKED = &H2000&
Private Const TV_FIRST = &H1100
Private Const TVM_SETITEM As Long = (TV_FIRST + 13)
Private Const TVM_GETITEM As Long = (TV_FIRST + 12)

Sub SetItemChecked(ByVal hTreeView As Long, ByVal hItem As Long, ByVal IsChecked As Boolean)
Dim tvi As TVITEM
 
tvi.mask = TVIF_STATE Or TVIF_HANDLE
tvi.hItem = hItem
If IsChecked Then
    tvi.state = GetItemState(hTreeView, hItem) Or TVIS_CHECKED
Else
    tvi.state = GetItemState(hTreeView, hItem) And Not TVIS_CHECKED
End If
SendMessage hTreeView, TVM_SETITEM, 0&, tvi
End Sub
 
Function GetItemState(ByVal hTreeView As Long, ByVal hItem As Long) As Long
Dim tvi As TVITEM
tvi.mask = TVIF_STATE Or TVIF_HANDLE
tvi.hItem = hItem
SendMessage hTreeView, TVM_GETITEM, 0&, tvi
GetItemState = tvi.state
End Function

Private Sub Command1_Click()
SetItemChecked 264210, 1, True
End Sub

SendMessage hTreeView, TVM_GETITEM, 0&, tvi

SendMessage hTreeView, TVM_GETITEM, 0&, tvi