That would work. However, be aware that WiFi hadn't been invented when Win98 was designed, so the operating system support for it is limited to the add-in drivers and supplemental WiFi client management utilities provided by the device manufacturer. Some security layers, such as WPA, are not available in Win98 unless you purchase additional 3rd-party software. If it were me, I'd hardwire the Win98 system to the router if at all possible. If that old system has now been moved upstairs/downstairs/whereever and you can't run an ethernet cable from it to the router, well, then you have to live with Win98's WiFi minor limitations.
I want to set up my main computer that is hooked up to a cable modem running xp pro with my older desktop running 98se. Can I just hook up a wireless broadband router to my cable modem and plug in a usb adapter into my old computer? Is there anything else I would need to buy or do? Thank's.