This is what I would do assuming the raid hardware is compatible:
1. I would get the Promise card and install it in the current system., with drivers...
2. Make a backup of your Maxtor-80GB. You may be able to zip the particions or subdirectories in raptor array, or to DVDs.
3. Stop system and move Maxtor-80 to new adapter, and see if the controller BIOS recognizes the array. I am not familiar with the Promise family, but I assume there is a BIOS menu for configuration. You will have to figure out the process. But basically, I would think, it either comes up recognized or not.
4a. If it does, great. Now you have some experience to move the Raptors.
4b. If not, you have to use the backups, but you may want to go ahead and use the Maxtor-80s to backup the other array to make the jump.
If you are not ready for the mobo jump, you can choose to move the drives back until you are ready, or restore them and leave them in the new adapter.
I am not sure if you need to give some consideration or not as to where (channel..) you place the Maxtor-80 drives bacause later on you want to have the Raptor as the boot array.
If all is smooth (and you are lucky) you may be able to make the jump without re-installing the system