MacBook permissions problem

Last May I had to have my HDD on the MacBook replaced due to it "falling off a table" in Brazil. Actually, it doesn't seem to have been that badly damaged as the repair guy was able to retireve some of my files. As nearly all of the others wrere backed up, I actually lost nothing.
However, the repair guy installed Leopard himself and gave me a username which is not the one I normally use.
As I really hardly ever use OSX, I didn't get around to this until very recently.
In any event, I created a new User and copied all my stuff over from the other User's home. I actually did this from Ubuntu and it allowed me to more conveniently access my Music files which are all on the OSX partition of my Mac.
However, in one of my brief ventures into OSX-land the other day, I found I couldn't download an updated version of Opera. In addition, I wanted to install Mozy on the Mac and had intended to install using the .dmg file I had downloaded in Ubuntu (and sent over via cl1p.net However, this wouldn't even download for me.
It turns out the problem was one of permissions.
Practically, ALL of my files and folders in my new Home folder had as own, not me, but _unknown which is presumably the name postumously given to the previous owner.
So, I had to go into HardDisk>>Users>paul and then GetInfo (right click -- or Ctrl-click -- on the folder).
Now, click on the padlock and enter your password in the popup dialog.
Next, open Sharing & Permissions at the bottom of the GetInfo box, highlight the single user row (where it says _unknown) and click on the "+" in the small box below. Choose your user name in the dialog that opens. Then highlight th_unknown row again and click the "-" in the same box to delete it. Now click on the small box to the right of the +/- box and select Apply to enclosed files.
Actually I found that this didn't always work for reasons I don't understand. Nevertheless, after I had changed ownership on all of the important folders, I was now able to successfully download and install Opera 9.52.