A little while ago I had the pleasure of moving a handful of computers that at one time had been part of a domain (which was no longer available) to a workgroup. This in itself is not a big deal but the problem was that every user had their settings which I knew could possibly be lost by doing this. It wasn't without glitches but here is what I did:
It is important that you first backup the current user. You should still be able to login to the computer under the domain which has all the correct settings for the user. Open up the registry editor by going to Start, Run and typing in regedit. Once in the registry editor click on the HKEY_CURRENT_USER and then export the entire key by going to File, Export and saving the file on the computer where you'll find it again if needed. I suggest creating a folder for this specific exercise (e.g. c:\temp\settings).
Next go to Start, All Programs, Accessories, System Tools and open The Files and Settings Transfer Wizard. Once the program opens click next and select Old Computer, click next and it will analyze your computer. Once you're at the Select Transfer method screen select Other, click Browse... and choose a folder where to store all your settings. Make sure it is in a folder that will be easily accessible and don't put it on the desktop or my documents folder as this might become unavailable after you've moved off the domain. Something like c:\temp\settings is a good idea. Click next and it will ask you what to transfer, select Both files and settings and click next. It will then collect all of your settings and save them to the folder you indicated. Once you've completed this, reboot the computer.
After the computer reboots, login in as Administrator. Once logged in open My Computer and navigate to C:\Documents and Settings. There should be a folder within there named after the username you want to switch over. For example, if your username on the domain was jsmith and the domain name was ABC then there should be a folder in C:\Documents and Settings called jsmith.ABC or maybe just jsmith. I suggest copying any user folder that contains jsmith. Right click the folder(s) and select copy. Then go to your backup folder and paste the folders. You should now have a backup of the registry, the Documents and Settings Folders, and the backup from the Files and Settings Transfer Wizard. Make sure if you use a mail program other than Outlook Express that you know the password for the email account because it might be reset after the transfer.
Note: Some program settings may not make the transfer. So if you're favorite program is setup just the way you like it you may want to try exporting the settings yourself or find which registry key holds that information.