Okay... so I'm not a regular, but I'm stunned nobody has answered this.
Yes, of course you can.
Easiest method is to set up how you want on a user account, then export the registry entries for that account to the default user.
More detail:-
Open RegEdit
Navigate to "HKEY_CURRENT_USER\Control Panel"
Export the folder from the tree.
Open the .reg in Notepad.
Find and Replace "HKEY_CURRENT_USER\Control Panel" to "HKEY_USERS\.DEFAULT\Control Panel".
Save and Exit.
Import the Registry file.
Relog... or maybe reboot, I can't remember.
I've done this many times for corporate branding of Domain Login. It's not hard. I usually make up an install script which I apply just before setting NewSID in the RunOnce and Ghosting a workstation.
BTW... this will transfer everything in the theme. Desktop Background (Wallpaper), Colour Scheme, Font Styles and settings... Even ShellStyle / XP Theme if you are using one. ^_^
hmm.... come to think of it, I'm not sure it is .default .... I've scripted the process heavily since I first developed it.

But that's the general idea. I'm sure you will figure it out and refine it to your purpose.