So you have Win98 already on a partition? or the full drive? If so are you able to "cut off"/create a new primary partition for XP? If so, do that, create a new primary for XP, which should automatically hide the Win98 primary, as there can only be one active primary in Microsoft land. Afterwards, install XP, this will undoubtedly overwrite your bootstrap and automatically always launch XP afterwards. To "correct this", install Smart Boot Manager afterwards (or a manager of your choice). This will make the bootmanager appear each bootup, and you can activate/deactivate the primary of your choice from then on.