I've had never been able to change the default settings for PDFCreator under Windows Vista: every option I changed would not be saved. I've asked about it in this forum a couple of times but never got any clue.
Today I had the idea of inspecting the Windows registry with regedit and, bingo! The program creates registry keys where my user is not allowed to write. If I look at the ACL of:
HKEY_CURRENT_USER\\Software\\PDFCreator
... I can't see my user. Instead, I see an unknown account entry for S-1-5-5-0-2215242. If I remove the keys, they're recreated with the same wrong permissions.
Solution? I added my user to the list and took ownership of the whole tree. Now I can finally configure the program to suit my needs. It evens remembers the last save directory!
I hope this helps someone else.
P.S. This might also apply to Windows 7, but I'm not familiar with it.