Nick, much depends on "how much" different hardware.
Since your client is running Exchange, you probably want to do a complete "rebuild" only as a last resort.
Since NT doesn't do a good job of detecting hardware, "transferring" the server CAN be problematic.
Two routes that I see you possibly taking:
1. Transferring the hard drive from the present machine to a new server.
2. Creating an image of your present server and transferring the image to completely new hardware. This route requires that you purchase additional software to create the disk image.
The biggest potential problem in either case will be IDE drivers. Since Windows (in general) only loads the drivers for the IDE controller it detects on your motherboard (or you tell it it needs, moving the drive (or an image) to a computer with a different IDE controller may make your drive inaccessible on that new computer.
Take a look at the following MS Knowledgebase article:
268066 - Startup Problems When Transferring System Hard Disk to a Backup Computer
The easiest way to prevent this type of problem is to choose a motherboard with the same chipset that exists on the present server (if at all possible).
As long as you can get the server to boot, you can then load any new drivers that apply to the new server.
Hope this helps.
