Since a well-crafted driver should support WMI, and since WMILIB isn't available in the original Windows 98, you might need to provide a virtual device driver (VxD) stub for the WMILIB functions so that your driver will load. Consult Appendix A, "Coping with Windows 98 Incompatibilities," for more information about writing a VxD stub. (The WDMSTUB VxD discussed in the appendix doesn't include the WMILIB functions, but the appendix describes how you might invent them.)
A number of bugs afflicted the WMI support in the original retail release of Windows 98. The updates to Windows 98 (Second Edition and Service Pack 1) fixed these bugs. (Or some of them, anyway. I have a laptop that runs Windows 2000 and WMI just fine, but WMI won't initialize under Windows 98 Second Edition on this computer.) Even so, the standard setup procedure doesn't install WMI by default. To install it yourself, open Add/Remove Programs in the Control Panel, select the Windows Setup tab, and request installation of Web-Based Enterprise Mgmt within the Internet Tools category.