Motherboard and Operating System

I had Pentium III 600Mhz system. I have upgraded my motherboard to ASUS A7N8X Deluxe with AMD Athelon XP 2100. I didn't format the hard drive because I thought it might work without formatting my whole hard drive. I have lots of stuff in my hard drive and don't want to delete eveything. If motherboard is chaged, do I have to reinstall the operating system? Is there any way to save my old stuff without duplicating the hard drive or buying a new hard drive disk? Or simply, just need to reinstall the operating system by formatting my HDD?

 

If it's 98/ME you should be able to run the same HD. Might be buggy though. Given the chance I'd reformat anyway just to get a good clean install. If you get it going "o.k." consider backing up your important files on removable media then reformat.
If it's win XP you will probably need to go through Windows Product Activation. This may even require a telephone call to Microsoft.