You may not get much luck from Microsoft, as they have totally discontinued Windows 98 since last June. However, note that WGA validation is skipped when using Windows 98, so if the key you use successfully installs Windows 98, you shoul not have any trouble. I mention this because you posted on a WGA forum.
Windows 98 perhaps skips validation since it predates product activation, and thus Microsoft may have been a little sloppy with managing their product keys.