It seems Vista prevents a program from writing a file in the Program Files folder with only a Standard type of User Account.
That is one of the principal security features of Vista -- Thou Shalt Not Write to Program Files.
This is why programs which have a truly automatic update feature (they actually rewrite their own data files) must be set to Run As Administrator in Vista and Win7. This is considered a cop out though, and programs written to work for Vista/Win7 are supposed to be able to run without Run As Administrator checked.
An overall design element of Vista is that you cannot truly login as Administrator. Instead, you login as the standard user and must elevate your privileges any time you want to do a task that is deemed by Vista or Windows 7 as an Administrator-only task.
Data is supposed to be stored in Documents and Settings under the appropriate user or under All Users. I guess for the time being you could do All Users and figure out user support later.
I find Vista UAC to be tedious at best and from what I have read of Win7's UAC, they missed the point people were making. Apple has UAC spot-on. Applications downloaded from the Internet get prompted. Installing software gets prompted. That's really about it. Tasks you perform every day such as launching older applications or moving folders to the desktop do not get prompted on Mac. They do on Vista.