Having trouble installing the MobileMe update that was just released? You’re not alone. The workaround at present is to sign out of .Mac (from inside System Preferences), and the sign in again. After a minute you should get a dialogue to open Apple Software Update.
If you don’t, download from the link below… I’m hosting the update until it surfaces on Apple’s Download Support page.
MobileMe Update for Mac OS X (8.3 MB)