I followed these instructions ((Guide) How to Install Win98se with 3dfx driver in Dosbox) to install Windows 98 SE under the latest yhkwong DosBox build (20120521). Host system is Windows 7 x64.

Windows 98 SE installed and boots successfully. However, the "3DFX Voodoo" device does not appear in Win98 Device Manager under "Sound, Video, and Game Controllers". Installing "vg-w9x-q3.exe" within Win98 and doing "Add New Device" did not fix the issue, even after several tries.

If it matters, the host system has nGlide 0.98 installed. As per the guide linked above, the dosbox.conf includes "glide=yes". I also tried "glide=emu", but no effect.