Is this an external drive or a partition on an internal hard disk?
If it is an external drive, I would recommend using UUID= in your fstab entry instead of the device, because the device might change in the future.
Try using udevinfo to gather the info you need.
First determine the device that is used presently. You can do that by monitoring /var/log/messages as you plug in the usb cable:
sudo tail -f /var/log/messages
Suppose that the partition on the drive is /dev/sda1. Then you can use udevinfo to determine what the UUID number is of the filesystem:
udevinfo -q env -n /dev/sda1
Note the line for "FS_UUID=". Copy the UUID number, then edit your /etc/fstab entry for the device:
UUID=<UUID #> /media/usbdisk vfat defaults,uid=yourusername,gid=yourgroup,noauto,fmask=0117,dmask=0007
Read the man mount page for more options. I used /media/usbdisk as the mount point, but the one you use is up to you. The "noauto" option will prevent the partition from being mounted on boot. Use this for removable disks.
If the partition is on an internal drive, then you can use the device instead, such as /dev/hda3 if that is what it is. In this case, don't use the "noauto" option.