mkdir /mnt/hda4 # You only need to do this once
mount /dev/hda4 /mnt/hda4
You can have this mounted at boot-time by adding this line to your /etc/fstab file:
/dev/hda4 /mnt/hda4/ vfat auto,user 0 0
You can then see your FAT32 device under /mnt/hda4.
You can mount the partition somewhere else by changing /mnt/hda4 everywhere in the above if you like.
Alternatively, most distros provide some kind of tool to set this up for you.