AS3 :: Flash - Simulate AS2 _global Variable Using A Simple Class?

I have recently started making (and am still making) the transition from ActionScript 2 to 3. I have used the _global variable in an AS2 project as I needed a variable to be accessible from within ANY swf loaded into my main movie. This worked like a treat.

However, along came AS3 and whipped that from right under my feet. After much Googling, a few people suggested making use of a simple class with a simple variable that can be publicly set and retrieved. I made a simple class, imported it and manipulated the value, and all went well, however the instance of the class I create in my main loader movie is still not accessible from within a second SWF that gets loaded into my movie. If I re-instantiate the class in the SWF that is being dynamically loaded, the value reverts to the default value in the class code, not the new value set in my parent (first) movie.

Here is my class code, stored in an external .as file, is there any way I can simulate the ostype variable being a global variable?

package{
public class ostype {
public var ismac:Boolean = false;

[code]....

it's used as a simple identifier as to what operating system this flash app is being used on (mac or windows) and as a result let's me server content - such as saving files - in a different manner.