somebody might want to correct me but I think if you preorder, you go into some sort of waiting list. When the next beta becomes availible, you can download it via impulse. I'm not so sure if the window for getting the beta is still open, someone from SD should be albe to confirm that.
Essentially correct. The beta as of 4 days ago was open, I am unsure of its current status. When it is open you get access when you buy it and will have access to all subsequent versions of the beta. If the beta is already closed or when the beta becomes closed, you wait for the next full beta version to roll around before you can enter. For example we a currently beta 2. On monday we will be beta 2a. If it is closed, you will not get in at beta 2a, but will get in at beta 3. At this time they don't know if there will be a beta 3 or if it will just be release, but I would imagine a beta 3, if they have one, would be in late feb early march. You can check with stradock sales to find out if the beta is open or go to the demigod irc between 9 and 5 EST and ask a dev. Hope that helps.