Thanks Duncan, unfortunately I don't have the means to backup so so many programs and files., I have the disk partitioned so when I did the re-install of XP a few weeks ago I only formatted the first partition to put the new OS on.
I have found this tip on TweakXP.com so hopefully it will work.
Before you swap out the current motherboard go to device manager and select the IDE ATA/ATAPI Controller and select your current
storage controller. Right click, select update driver and select install from a list or specific location. Click don't search I will choose the driver to install and select the standard dual channel IDE controller.
This will prevent the inaccessable boot device blue
screen. I have done this multiple times on different platforms with no problems.
Also I found that booting the first time with the new motherboard is best done in the Safe mode where XP will install the
drivers it needs and at the same time you can install the new motherboard drivers from its CD.