I don't believe partimage works with ext4 partitions, so if your RHEL is formatted that way, you'll need to use another tool. I believe dd handles ext4, and possibly also clonzilla.
If your partitions are both ext3, you could use partimage. Simply clone each partition -- saving your images one at a time. Then restore them to the new hdd. First partition and format the target drive with something like gparted. Make sure the partitions are the same size or larger than the source. Then you can restore the images to the target drive one at a time.
If you need something more automated, or something that will clone the entire drive into one image, then a proprietary solution like Paragon is probably required.
However you clone your drive, some manual tweaking will probably be required: adjust /etc/fstab for different UUIDs, update grub, possibly restore the mbr etc.