Hi,
By default you will get a limited listing from clicking the top level vcenter container on the left hand pane and on the right-hand pane click "tasks/events"
To my knowledge not a complete historical listing of all the changes can be found direct in vCenter see so will need to interrogate the database :
if using vCenter 4.x
http://www.vmware.com/resources/techresources/10087
vCenter 2.x
http://www.vmware.com/resources/techresources/759
relates to vCenter 3 / 4.x but haven't seen anything to appear'
http://communities.vmware.com/thread/176870
There is some v.powerful powercli scripts out there though - check out Lucd's site - example below:
http://www.lucd.info/tag/event/
Many tx!