If you are looking for routing between 2 networks in Windows 98SE yes it can do it. Its called ICS (Internet Connection Sharing).
But from what you add afterwards: "that it would be nice if win98 started using the other IP address on the fly" I understand that you don't want routing between networks but for the same computer. Yes it's possible by looking up the routing map in a command prompt (by typing 'route print') you should see both Adapters in the table called with different Interface. Now what matters is the Metric on each Interface the one with the lower metric is always used last (e.i. when the one with the higher interface does not respond, because its unplugged). So the only thing you will have to do to make sure that Win98 dosn't use the Wireless card when the regular is plugged in, is to change the metric of the Wireless card to a higher number than the Wired card.
You can change those entries by using the Route command. But this is a very long process. I think you can do it in the registry but I'm not sure where. You should look it up on the Microsoft web site.
