If you’ve just installed the 1.1 upgrade and launch it for the first time only to find it devoid of all your images or a collection of just a few or older images you most likely did not have your prior working database in the default location:
Documents and Settings/[username]/My Documents/My Pictures/Lightroom
It seems 1.1 just looks to the default installation location for your old database file. If there is one there it converts it to 1.1 and opens. If there is not one there it just opens empty.
Take heart! You just need to locate your actual database, and point Lightroom 1.1 to it. It will then convert it and open where you left off in version 1.0.
On Win: Hold the Ctrl key and launch Lightroom
On Mac: Hold the Alt key and launch Lightroom
When the Select dialog opens, navigate to your old database file, click it and choose Select. You should be all set.