Back up your photos, that is the safest.
Don't forget if you try to install XP it will look for the available partition, so it will look to the partition that you have your photos.
If you want a dual boot partition the 98 into two partitions, providing that there is adequate space to host both the operating systems.
Or if you want to just have XP boot with with 98 floppy and format the 98 partition, installing XP having formated, which will by default be the active partition.
If your photos are really important, don't mess around until you have backed up your files.