[d'Wooluf]

I'm not sure whether I want a totally appliance-like xbmc. Following on from the guide that patseguin posted the link to, I had a look at the wiki page that KRKA01 linked to. I found the following instructions:

1.Log in as administrator.
2.Open the start menu, and type in the search box: mmc <ENTER>.
3.Choose File -> Add/Remove Snap-in....
4.Select Group Policy Object Editor and hit Add.
5.In the wizard that pops up, hit Browse..., go to tab Users, select your user account (the one that you set up to log on automatically in step 1) and hit OK.
6.Make sure that the checkbox in the wizard is Unchecked, and hit Finish.
7.Hit OK in the Add/Remove Snap-ins window.
8.In the User Configuration -> Administrative Templates -> System folder, open Custom User Interface.
9.Select Enabled and enter the full path (including XBMC.exe and any switches that you may use) in the Interface file name textbox.

The difference is that you can make xbmc the shell for just one account (instead of all of them) and leave explorer as the shell for the other accounts. So I've set up a standard account named xbmc with xbmc.exe as the 'Custom User Interface' and I haven't set up a password for it. This means that when someone in the house boots up the computer they see an xbmc account. It's just one click with the remote (err... hopefully- need a remote to test that part) or 'Enter' on the keyboard to get into xbmc. I don't think one button-press is too much to ask. It means that the other accounts are accessible for admin or anything else that needs to be done.

The user can reboot the machine from xbmc if they want to do something else. A logoff option from xbmc would be nice, but overall I think this just might work for me.

Edit: this was all tested on Windows 7 Ultimate. Not all editions of Windows may come with the group policy editor.