Windows 98 is notoriously unstable on modern hardware without the right emulated devices. For a "full" experience, use these settings in your QEMU startup script: installing windows 98, windows xp, and starcraft in qemu
The default VGA driver is 16-color hell. You need or the NVIDIA Detonator 3 (for emulated S3 cards). Install this to achieve 1024x768 at 32-bit color. Without this, your "full" experience is only half-full. windows 98 qcow2 full