RSData was (is?) an ActiveX designed to bring DDE/OPC data into other applications, such as Access. It was part of the RSTools product and also shipped with RSView32. You can probably download a copy from Rockwell or maybe someone else on the Forum has a copy.
Here is a document link to RSTools. The AB Part Number is 9399-TOOLSGR. I didn't find it available for free download so you'll probably have to purchase it if its still available.