I browse lq.org fairly frequently and have some rudimentary experience with linux but have never posted. You describe a problem identical to one I have experienced so this might be a chance for me to help.
Can you access your drive as root? If so, it may be a problem with permissions, if not your fstab may need looking at. SuSE/Linux registers my usb enclosure as a scsi device and assigns it the (default) mount point /media/sda1. But I had a lot of trouble tweaking the fstab before I could make it work.
As far as I understand, you should be looking for (in your /etc/fstab) a line beginning with "usbdevfs" and a line beginning with "/dev/sda1", although you may have two of each seeing as you have 2 usb drives. If you post the remainder of each line I can compare it to my working fstab and maybe see whats going wrong.