The hard drive was connected to Redhat9 Linux via firewire and the hard drive had a reiserfs filesystem. It was supposed to be used for backups, but suddenly stopped working (it was not anymore recognized during system startup). Probably that had something to do with the external USB zip drive. Both are apparently visible to the system as SCSI devices and the zip drive might have (via automount) occupied the sda number that was manually added to /etc/fstab to enable the Maxtor hard drive. To check whether everything is OK with the drive itself, I connected it to my work computer. My work computer, however doesn't have a fire wire card, so I had to use the USB port. This shouldn't make any difference as both USB and firewire are somehow treated as SCSI devices.
I only edited /etc/fstab adding the following line:
/dev/sda1 /mnt/usbhd1 reiserfs defaults 1 2
I first forgot to create the directory /mnt/usbhd1. Thus after restarting the drive was not mounted. I checked with /sbin/fdisk -l and there was the following entry
/dev/sda1 Windows 95 (or something like that)
Funnily the resiserfs file system shows as a fat filesystem. I changed the "reiserfs" entry in /etc/fstab to "vfat" and created the directory /mnt/usbhd1. During startup there was an error (something like "no fat filesystem could be found on the partition"). So I changed it back to reiserfs, rebooted and the external drive was mounted during startup without problems.