Check out the VB6 Runtime files. I think it might be in there. If it's not then it's in some other package. If you send them the file, the can put it in the system32 folder, but they still need to register it. Look here on how to do that:
http://www.ascentive.com/support/new...e=MSWINSCK.OCX
If you don't like that explanation, google the topic, theres tons of results. Depending on what other errors you get, if it's more missing files, then you are probably going to need the runtime files put on any machine running the client.