Can't write to external usb drive as normal user despite efforts

[keitho@strucktower.com]

I have an external usb drive on which I have a fat32 formatted partition.
I can't figure out how to mount it so that I can write to it as a normal
user.

Here's what I have tried (with no fstab entry):

keith@eve:~$ sudo mount /dev/sdb4 -t vfat /usb
keith@eve:~$ mount
 [snip]
/dev/sdb4 on /usb type vfat (rw)
keith@eve:~$ touch /usb/test
touch: cannot touch `/usb/test': Permission denied
keith@eve:~$ ls -al /usb
total 20
drwxr-xr-x  2 root root 16384 Dec 31  1969 .
drwxr-xr-x 26 root root  4096 Nov 22 22:13 ..
keith@eve:~$ sudo chown keith:keith /usb
chown: changing ownership of `/usb': Operation not permitted
keith@eve:~$ sudo chmod 750 /usb
keith@eve:~$ ls -al /usb
total 20
drwxr-xr-x  2 root root 16384 Dec 31  1969 .
drwxr-xr-x 26 root root  4096 Nov 22 22:13 ..
keith@eve:~$ ls -al /bin/mount
-rwsr-xr-x 1 root root 84944 Aug  3 10:02 /bin/mount
keith@eve:~$ groups
keith root sudo audio

I have also tried this with various different fstab lines to no avail.

There is a relevant discussion of this kind of problem here:
http://www.linuxquestions.org/questions/debian-26/mount-a-500gb-usb-hard-disk-permission-issues-609218/

Can someone illuminate me on how to mount this external usb drive so that
I can write to it as a normal user? Reading through the man pages hasn't
helped me yet on this problem.
Thanks,
keith