Use the ShellExecute API function.
VB Code:
Private Declare Function ShellExecute Lib "shell32.dll" _
Alias "ShellExecuteA" (ByVal hwnd As Long, ByVal lpOperation As _
String, ByVal lpFile As String, ByVal lpParameters As String, ByVal _
lpDirectory As String, ByVal nShowCmd As Long) As Long
Private Sub OpenFile(sFile As String)
ShellExecute Me.hwnd, vbNullString, sFile, vbNullString, vbNullString, 1
End Sub
Private Sub Command1_Click()
Call OpenFile("C:\MyFile.txt")
End Sub