I go to the maker's site or I use/order the restore media for the laptop or desktop.
The ECS web site noted at least 2 or more versions of that motherboard. http://www.ecs.com.tw/ECSWebSite/Product/Product_Detail.aspx?DetailID=392&MenuID=1&LanID=0
Remember that for XP we have some extreme issues about how we must install drivers in a specific order. That order has not changed in over a decade so I'll not duplicate that here.
You'll have to identify the version of the board to get the right drivers.
I work on so many different computers and finding drivers is so hard sometimes. Everyone wants you to download driver software with a fee. Is there any easy way around this. I am working on a pc that was made by a company for Home Shopping Network, one of those no name deals. I need to update the video drivers because the screen colors are twisted. I tried removing the card in safe mode so it would redo the drivers but it wouldn't let me. I tried going to motherboard Elitegroup for drivers and that's where I got smart tweak and just uninstalled it because I couldn't find the monthly fee. So where else can I get the drivers for a motherboard 661fx-m, Win XP Home?