Yep, BIOS is cumulative, just need the latest.
You can use whatever is on the disk but I prefer downloading it from the manufacturer, always get he latest that way:
http://www.asus.com/product.aspx?P_ID=KjpYqzmAd9vsTM2D
Just select your OS and find it under BIOS-utilities.
If there's no difference in color-coding it's perfectly possible only the northbridge has a HD-controller, so then you would only find a single option.
I think you also have EZ flash; it's a utility build into the board that let's you update the BIOS without running something from an external device (floppy, USB stick). If you start that up (apears as an option under 'tools' in mine) you should be able to flash it there too.
Don't think it really matters which utility you use. I've flashed BIOS' from floppies, USB sticks and from Windows on all kinds of boards without any trouble, but you need to make darn sure that the file you want to update with isn't corrupt. That's the risk: flash it with a corrupt BIOS and that board is toast.
* if it comes down to either that Afudos or EZ flash, I'd go with the latter.