There are a few things you need to worry about and / or do before you make the move.
 
Upgrading
 
- If your planning on upgrading your system to Windows 7 or above make sure to run the Microsoft compatibility tool they have to tell you if you computer is eligible for the upgrade.
 
- If the upgrade is not something you want to do then read on...
 
Reinstalling XP
 
- You might want to image your current drive state that way if anything goes wrong you can roll back to your current configuration. There are a lot of great apps available to help do this. Norton Ghost, Macrium Reflect, Acronis True Image, etc...
 
- Next, backup all your data, if any and all your DAW presets, etc...
 
- Format your hard drive and reinstall Windows XP. Install all your system drivers. Install all the Microsoft Service Packs and Windows Updates. Install the latest video card drivers and download the latest drivers for your soundcard or audio interface.
 
*** Important: Make sure you have the latest BIOS installed for your motherboard as well.
 
- Install Sonar and all the updates and patches.
 
- There is information available to optimize Windows for a DAW system. Do a Google search on this and follow the steps.
 
Conclusion
 
You should be in business after that, might take a long time but it will be well worth it. From here I would create an image of the new system configuration. That way, if you need to do this again, you can just get a new hard drive and load the system image to the new hard drive and your back in business minus a few Windows Updates you may have to do :) Saves hours of time and effort, trust me!!!
 
Hopefully this is along the lines of the advice you were looking for.
 
Also, a great site to get all your tools at once: http://www.ninite.com/ it’s great! Antivirus, Malware, Flash, etc... All in one easy download file :)
 
Good luck and happy computing I hope you make an easy decision based on everyone’s input and of course it always comes down to money in the end doesn’t it?