I'm studying for my ccna exam and I need a simulator to do the practise questions. I've tried the newest boson 5.25 and 5.27 avialable for download on the web, but somehow my computer crashes whenever starts the simulator. some one told me that the older version 5.19 or 5.12 may work better. I can't find these older version anywhere. is somebody has them and can procide me a download? thanks a lot.