if you want to start win98 you could check the bootmanager. As you have SUSE and XP on your box I think that SUSE took over the bootmanager part. I don't use SUSE but I remember that YAST is the central config tool. So you should start it and search for "boot configuration" or a similar thing. There you should be able to add the secondary drive to the boot menu. After restarting there should be a new boot-item. Remark: I'm not so sure that you could start an "alien" win98 on your box - except the orginial box had the hardware like of yours
If you just want to use the secondary drive as storage then YAST surely has a tool to configure partitions (in /etc/fstab).
Hope this helps.