The rpcrt4.dll is part of the DCom98 package. I have seen other problems, unrelated to LabVIEW, with this .dll arise when other programs have installed different versions of some of the DCom DLLs. You may want to consider trying this program out on another Win98 machine, or you may want to search through the Microsoft Support page for errors with this dll, specifically with the error number in the message you receive. The ones that I have seen have suggested restoring the DCom dlls to the original ones from the Win98 disk. There is also an update to the DCom components for Windows 98 (version 1.3) on the Microsoft website.