How'd you do it?
Unlike the previous poster's reply, yes you can. I've done it, it works fine.
However, I would really recommend that you don't upgrade to beta 1 unless you are developer. Most third party apps have issues with 4.2 beta 1.
Wouldn't agree there. I regularly use about thirty apps on ios 4.2. Only one thid party app has caused any problem. It's reall stable for a beta1
I upgraded rather than restoring and have found it to be very unstable.
-Settings only works about 30% of the time.
-Applications often fail to launch.
-The OS seems very slow.
Last night I did a restore to 4.2, restored my backup, sync'd files etc... and now it runs great!
So I'd have to recommend doing a full restore rather than an upgrade.