If you are on Solaris, you can use this:

find . -user username -print


This will display all the files in the current directory with the owner of "username". If you cant to find all the files in the system, you could change to the root dir and use that command.

Ex:

cd /
(type "pwd" to see if you are in the "root" directory, it should come up with just a "/")
find . -user username -print