You could image over over your old OS using Acronis True Image and Norton's Ghost. When the new system boots, it will hunt desperately for new drivers and will find many. Afterwards, you'll need to manually download some for the machine. If you are using a retail version of XP, you will probably need to revalidate the XP, but if it has been years since you last validated, Microsoft will either do it automatically or with a phone call. Tell them that you swapped mother boards if they asked.

Devistification is pain in the neck. I am going through it with an HP. I got most of the drivers sorted (without any help from HP whose website takes the Microsoft party line that Vista is better and we won't help you make a "mistake"). Some of the easy stuff was to locate the most similar XP machine they sold and download those drivers. I am still, however, without any sound because I can figure out the correct sound driver for this machine. I might have to buy a sound card and that will irk me.