How much "different" is the new motherboard compared to the old motherboard?
If the chip-set and on-board features are of the same manufacture, it might work as is.
One option is to have your old hard drive as the C: drive, boot from your XP CD and perform a repair installation.
As far as a clean installation, there are no easy ways to transfer your old programs onto a new hard drive with a clean installation of XP.
XP's file and settings transfer tool requires either a running PC, or a prepared transfer file.
Most of the other program relocation tools out there also require a running PC as the source.
As to MaxBlast, use EXTREME caution if you decide to run it.
DO NOT run in automatic mode.
Make sure that you do not install the drive overlay software.
As far as I know, the copy utility in MaxBlast and WD's Data Lifeguard Tools are designed to copy drives and partitions not specific files or folders.
Even if you were able to copy over just your data files and the Program Files folder, your applications would not be recognized by XP and many would not run.
What would be missing from a simple copy operation would be the registry entries and system files that many programs install.
If you want a clean install of XP for your new motherboard and hard drive, (which I fully agree with) you are going to have to go through the process of reinstalling all of your applications again.
You can copy over and import data files from the old hard drive.
Some programs will install a little faster and recover your user preferences if you copy over their installed folder.
Summary:
Install XP clean onto your new hard drive.
Install at least SP1 for XP and most if not all critical and security updates.
Copy your data files from the old hard drive.
Import your mail and favorites.
You can copy the Program Files folder contents onto the new hard drive.
Use caution with folders that already exist.
Do NOT replace existing files.
Reinstal