Host: Ubuntu64, 4GB RAM, Core2Duo E6600, Samsung HD502IJ
Guest: Windows XP Home, 1GB RAM, 8GB virtual disk
Benchmark Software: SiSoft Sandra Light, HD Tune

Short benchmark of this both VM

*) Dual CPU Mode

Resumee

VirtualBox shows better computing performance, which benefits for desktop applications and multmedia based operations. Interesting: the dual CPU mode in Vwmare has no advantage over the single CPU mode.
Certainly we can say: Virtualbox for desktop applications, Vmware for server but for the combined performance VMware ist the winner.

Don’t forget: Flash != Flex. Flex uses elements from Flash but is built on own classes. If Flash and Flex should play together we need a interface.
MovieClip is a display object in Flash and UIComponent is a display object in Flex. But we can wrap a MovieClip into a UIComponent, so the Flex UIComponent becomes a container for our Flash MovieClip.
Here both files, at first the MXML file:

And the Actionscript file with the class:

package {
	import mx.core.Application;
	import mx.core.UIComponent;
	import flash.display.MovieClip;

	/*****************************************************************
	 * File: FlexApp.as
	 *****************************************************************/

	public class FlexApp {
		private var _app:Application;

		public function FlexApp(app:Application) {
			_app=app;

			var btn:MovieClip=new BtnStop();
			var flexui:UIComponent=new UIComponent;
			flexui.addChild(btn);
			app.addChild(flexui);
		}

		static public function initApp():FlexApp {
			return new FlexApp(Application(Application.application));
		}

		public function get app():Application {
			return _app;
		}
	}
}

How it works

applicationComplete in the MXML file is the eventhandler called from the application. Here we provide our handler, which must be a static member function of a class so it can be called later.
initApp() creates our class and passes a application object to the constructor.
Inside the constructor we create the MovieClip from the imported Flash symbol “BtnStop” (this symbol comes from a swc lib, created with Flash). Then we create a Flex UIComponent container and add our MovieClip as a child. The UIComponent can now be added as child of the Flex application.

Overview of development tools for Flash/Flex

Close Eclipse and copy the complete Flexbuilder folder (standalone or plugin) inside this “dropin” folder. Restart Eclipse and now you should have the complete Flexbuilder envoirenment available!
Flexbuilder can be found with the default installation path at C :\Program Files\Adobe.

My recommendation:

For debugging, visual design of MXML: FlexBuilder
For mostly coding of Actionscript under Windows: FlashDevelop.