In Windows XP or 2000 (mostly in XP) environment, I cannot record or save projects when I'm not logging on with default user/administrator. Why?

It is because StreamAuthor will set up a default folder with the same permission of installer's "My Documents". Other users without permission to access this folder may get blocked from Windows mechanism.
Please go to StreamAuthor Menu: [Tools] -> select [Options] -> select [General] tab -> Make the "Default directory for opening/saving projects:" a general folder that every user has the permission to access.