Permissions

Question

Please could someone help / explain this permission problem to me.  It will be vague but I hope its a fairly common problem.
In order to get a recent project to work I changed the permissions of the parent database so that I was the owner.  This worked fine for the project in question.  When I went to finish some other ones that I was doing, I kept getting the 'attempt to attach an auto-named database... a database with the same name exists, cannot be opened, or is located on UNC share.'  This was on projects that previously worked without any problems.
My questions are:
1.  If using original settings, when an application is created, who is the default owner?
2.  Is there an easy way for me to revert to the previous settings?
3.  Is there a log anywhere of what has been changed previously?
Any help on this matter would be greatly appreciated.  Thank you.