OS specific, so you may have difficulty with that requirement (not saying it isn't possible).
But in any case, this is a better place to ask:
Flex not providing any direct access to windows system32 directory as it is OS specific but we can achieve this in our own way
1. You can use the File.desktopDirectory.nativePath to get the path string
2. You can cut the first three letters those will represent your OS installation drive e.g. x:/, generally its C:/ but not in all case so we do like this.
3. Now you can append your string to this like driveletter + "WINDOWS/system32"; and can call a method for File to resolve this
Below is an example to help and clear you more
var sFile:File = File.desktopDirectory;
var appPath:String = File.desktopDirectory.nativePath;
var driveletter:String = appPath.substr(0,3);
trace("OS installed Drive: " + driveletter);
sFile = sFile.resolvePath(driveletter+"WINDOWS/system32");
This will result you in your system32 path and may help you in your problem.