user access to FAT partition - help !

[Pierre TILQUIN <tilquin gena ucl ac be>]

Hello,

Does anyone know how to make a FAT partition writeable to someone besides
root.  
It must be a FAQ but I can't find the answer anywere.

As you know, the command chmod doesn't return errors but doesn't do
anything either; and an 'ls -l' shows no 'w' permission for other users
than root. I found something about fstab file and mount command.

In my /etc/fstab file, this partition is as follows :
/dev/hda7   /export/home   vfat   defaults   0 0

and calling mount command prints :
/dev/hda7 on /export/home type vfat (rw)

So it must be read-writeable but it isn't.

I modified /etc/fstab according to specific options of the mount command. 
/dev/hda7   /export/home   vfat   gid=440   0 0

But I didn't manage to set all the partition writeable to all users of
group 440. By default, the user is root.
Could anyone help me ?
Thanks in advance

Pierre