Sorry for the late response. I can't give you very specific instructions, since my dual boot Linux/Win 98-machine is *errh* temporarily out of service. (The computer I'm typing on now is Linux only.)
To mount a partition, you must have a place to mount it, this 'place' is just an empty directory. You must also know who should be able to read and write to the FAT partition.
If you only want to mount it once, root could issue a command to mount it:
# mount -t vfat /dev/hda3 /mnt/win
The '-t vfat' is for mounting a vfat partition. Next parameter is the partition to mount. If you don't know the partition name where Windows lives, you could see this with the command:
# /sbin/fdisk -l
The last parameter to the mount command is an empty directory to mount at. This directory could be pretty much anywhere in the file system.
To mount a partition automatically every time you boot into Linux, you must edit the file /etc/fstab and add a line with the mount options. This is a little more complicated. Since there is no "file owner" concept in FAT you must add parameters to the mount about who should be able to read and write. I can't give you the correct options, but try searching a little here:
Good luck! If this doesn't help, come back here and ask more. I'll try to be a little quicker replying next time