I will lay you a dollar to a doughnut that the external is formatted NTFS. The last three I bought were NTFS out of the box. Not all distros include NTFS support by default.
The error message
fs and ntfs is not supported by the kernel
seems to be imply that the drive is visible, but NTFS support is not available.
I would suggest that you run
from a terminal as root with the drive connected. That should tell you whether the system is seeing the physical drive.
I have no experience with RHEL 4, but this article
seems to imply that it is capable of mounting external drives (at least thumb drives, which are the subject of the article), but that they must be mounted through the command line, not automounted.