There are a number of differences. The ones probably affecting you are improved support for USB devices and the introduction of Internet Connection Sharing in 98 SE.
Simply put, your current operating system does not meet the system requirements for the hardware/software you just bought. You can either upgrade your OS or locate alternative products that will work with the OS you have.
Have purchased new hardware/software that says will install on Win98SE or later. What is the difference. I have Win98 and want to use these new products?