Расположи на форме textbox и button. Путь, естественно, пиши в texbox'е.
Option Explicit
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
Const SW_SHOWNORMAL = 1
Private Sub Command1_Click()
Call ShellExecute(0, "open", text1.text, "", "", SW_SHOWNORMAL)
End Sub