You can also do it directly from Windows if you prefer. The steps are simple:
1) Go to Asus' website, look for your motherboard model and download the latest BIOS.
2) Open the ZIP file and extract the .rom file anywhere on your hard drive.
3) Run (or install from CD) Asus Update, and select "Update BIOS from file".
4) Select the .rom file you downloaded and let Asus Update do the rest.
I've followed this procedure successfully two times already on my P5B Deluxe.