可以把Form的ToMost属性设置为TRUE;
或
用API函数:
Private Const GWL_HWNDPARENT As Short = (-8)
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hWnd As Integer, ByVal nIndex As Integer, ByVal dwNewLong As Integer) As Integer
在Form1里
dim frm as new Form2
SetWindowLong(frm.Handle.ToInt32, GWL_HWNDPARENT, Me.Handle.ToInt32)