Customize Boot.wim

Hi

I am using WDS to deploy our Windows XP SP3 images. I would like to
customize Boot.wim so I don't have to enter location, keyboard layout and
domain username/password everytime.

I have found some samples of Unattend.xml but I am haveing difficulty
figuring out what to do.
I don't need a huge and fancy Unattend.xml, just the settings above to make
the process a bit easier.

When I have a Unattend.xml is it enough to mount the Boot.wim image and add
the file to root of the image and commit the changes?

/Lasse