I take it you were asked to provide administrative rights to overwrite the files?

I don't think that the default location for for FSX in Vista and Win 7 is not the best place because of the security restrictions that those OS's have. I have heard that installing it to "C:\Microsoft Flight Simulator X" is a better place to install FSX. I've been lucky that I have more than one HDD so that I can install it where-ever I want to, away from those security problems.

Mark