As alexanrs has mentioned, most hardware that what was around by the time that Windows 98SE was introduced (which was on May 5, 1999), would have drivers that is included with Windows 98SE.
For a broad summary of what is supported, refer to the following link: http://en.wikipedia.org/wiki/Windows_98#Windo … _Second_Edition (the Windows 98 Section Edition section)
However, my experience is that the drivers included in Windows 98SE (or any Windows version for that matter) are just stock standard drivers to get your hardware working (without any additional functionality or features).
The drivers released (an updated) by the manufacturers sometimes includes additional functionality, features and also bug fixes.
A good example are your graphics drivers released by your various manufactures. With the stock driver, you rarely have additional tabs under your Display Properties but, if you install the manufacturer's driver, you do get those tabs that offers additional features (settings).
Whenver I installed Windows 98SE, I always made a point of updating my drivers to the latest version for compatibility & stability reasons, as well as bug fixes.