Am I right in thinking that both the guest account (which is no use anyway) and the admininistrator accounts are disabled by default this time around?
I haven't yet read any processes for getting into an admin account on Vista, I suspect the old ways from XP no longer work and you might actually be looking at reinstalling. (which will move your entire filesystem into a folder called WINDOWS.OLD so you won't actually lose any data, but you will lose full functionality from installed applications as well as any settings you may have made.)
This worked on earlier Beta's. I have not tried it on RTM or later Beta's but it might still be OK.
After the aurora shows up on first boot after setup, hit Shift-F10 and a command prompt will show up. If not hit ALT+TAB to select it from the pop up. Type "taskmgr" and hit Enter. In the task manager, close "msoobe.exe" (End Process). Windows will either log off or reboot. You will then login as Administrator. You can then enable the true Administrator account and also disable the requirement for passwords (Go to run, and type Control Userpasswords2, and then go into Advanced/advanced/users.)