1. Why are you running Jaguar Beta? Final has been avaliable since August 24th and several updates have been released since. Have you been living in a cave for the past few months?
2. Login screen is an option, you can turn it on and off in Preference Pane > Accounts. You can have it auto login a particular user, present a list of users or Name/Pwd prompt ... disable restart/shudown buttons on login screen ... blah!
3. What build of Jaguar Beta did you install? If it is one of the earlier builds then the problems you are seeing qould be normail for beta software. Personally, I would not risk installing a beta OS on my main machine unless it was the GM or really close to it.
4. What to do? You can not downgrade using your 10.1.x disk directly, so you are going have to boot from the original 10.1.x CD that came with your computer, initialize the disk and do a comletely clean install. Of course, backup all you important data to an extenal firewire drive, online storage or optical media ... or anywhere. A good idea would be to walk down to your local CompUSA (if there is one, I would have to walk for about 3500 miles on water ... even Jesus could not do that) and spend $129 on final version of Jaguar if you really need it.
> The above was by no means a flame, I tend to be very cynical and srcastic at the end of my work day (17:48 here). Hope it helps.