Quick searching says that VirtualBox does not have Guest Additions for Windows 98. Guest additions are used by virtualisation software to add things like sound drivers and smoother mouse movement.
VMware Player is another virtualisation platform that does have tooling for Windows 98. But honestly, rather than trying to virtualise all of Windows 98, you may have better luck with DOSBox. It's a program designed for your exact scenario, wanting to play old games. You may want to check out the community for DOSBox and what they can say about your old games.