A: 

Does this user have his/her own windows User? (his/her own account on XP). It should keep settings for you if you have them as a separate user from whoever else likes the larger DPI. Just create a user.

Sivvy
I have found that is not the case, possibly due to the way that group policies are implemented on our domain. I cannot alter these policies easily without an official request for change, long tedious process etc. Furthermore, I do not need to change the DPI, I need to change the font sizes in the appearance settings along with some of the colours.
Alex
After making those changes, have you tried saving them to a theme? Themes are easier than registry changes, or getting a user to do something they don't want to.
Sivvy
This might be of use as well.http://msdn.microsoft.com/en-us/library/bb773190(VS.85).aspxIt shows how to actually create .theme files.
Sivvy