You should be able to dual boot Windows 98 with XP if you are using the same File System. (FAT32)
But even if you are not you should be able to see Windows 98 from XP.
To view the startup options you will need to right click the My Computer icon the go to properties. I can't quite remember what tab you need but one of them contains the start up and recovery options. That will tell you what OS's you have installed and what one is the default to boot first.
I hope this is not too technical