Comes with XP SP2, I believe
File Description: Setup Custom Action Dll
Product Name: Microsoft® Windows® Operating System
Copyright: © Microsoft Corporation. All rights reserved.
Company Name: Microsoft Corporation
Internal Name: custom.dll
Original File Name: custom.dll
Path: \WINDOWS\SYSTEM32\TSCUPGRD.EXE
File Version: 5.1.2600.2180 (xpsp_sp2_rtm.040803-2158)
Product version: 5.1.2600.2180