XP SP2 would "not be publicly available for download" and only "invited beta testers and Microsoft TechNet subscribers" would be provided access to the bits, in reality it seems the bits - intentionally or not - are hard to guard inside the cage.
As can be seen apparently on some Bittorrent trackers, and a multitude of http/ftp file mirrors.
There's also supposedly a discussion over there about how to do unattended installations of this IE7 Beta1 that is "not public", and also the implications of Windows Genuine Authentication (WGA) and the wonders of hex editors. Not that we tried any of this, and in fact we warn you against it.
In fact, before you risk messing up your system, breaking IP, moral and Volish laws, we suggest you first read some of the reviews that are popping up, one of which says "The biggest problem with IE7 is that there isn't much different. The only differences I could really notice were the tabs, feed discovery, and phishing filter (which doesn't obviously do much)". So, YMMV. µ