You don't need to be root to mount the drive, but you do need to be root to set it up. I hope this is step by step for you:
1. Log in as root or su into root
2. You want to make sure that you have the usb drive plugged in, and that you have the following enabled in your kernel:
*USB mass storage
*UHCI, OHCI, or EHCI (if you're using 2.6)
*General scsi support
*Support for scsi drives
You can do them as modules or enabled. I don't like dealing with modules so I just enable it. Personal preferance--some people notice a performance difference, but it's too much of a hastle for me.
There is plenty of information on this forum to learn how to compile your kernel, so I won't go into that.
3. As root, type the command (in a terminal like konsole, xterm, aterm, or eterm)
a bunch of information will scroll by. Scroll up and look for something that says USB mass storage drive found on scsi blah blah blah. It should also tell you whether it has been assigned as sda, sdb, or sdc. I'm not at home so I cant post what it looks like. I'll try and come back and edit this for more details so you know what to look for.
4. You are still root, at the prompt type the following commands:
open a text editor (I use gentoo and I really like nano as a cconsole text editor) and edit your file called fstab. This file is a list of mount points (in the most general sense)
and enter this line, where location is replaced by your result of dmesg:
/dev/location /mnt/usbdrive auto rw,user,noauto 0 0
Remember location needs to be something like sda1, sda4, sdb1, or sdb4, etc. If the hard drive has a vfat file system, it will most likely be sda4. Otherwise, your chances are sda1 will be the answer, especially if it is the only usb device you have plugged in.
As root type:
If you don't get any error messages, then you are good to go. Then type"
Exit root, and you should be good to go.