I recently just used the Lightroom 4 trial and it moved my catalog information onto Lightroom 4, but now I need to use it in Lightroom 3 but none of the pictures are showing up in Lightroom 3? How am I able to use the same catalog now back in Lightroom 3?? Help! Thanks!
When you upgrade your catalog for LR4 it makes a copy. This LR4 catalog will not be able to open in LR3. Your original LR3 catalog should be unaffected. Make sure when you open LR3 you are pointing to the original LR3 catalog.
Assuming you've still got some time left in the LR4 trial, here's a way of saving the edits you did in LR4:
Step 3 won't work if the images have develop settings in Process Version 2012 (LR4's process version), which is why you need to use LR4 to convert the process version to 2010.
In the worst case (you've run out of time in the trial) you simply have to import any new images that you worked on only in LR4 into LR3 and do the edits again. In LR3, use Import, navigate to wherever you put the new images, and choose "Add". You just won't see the edits you did in LR4. Or if you do, they might not be right, as LR3 doesn't understand LR4's new process version.