Windows – Get full control over every file/dir in a drive

I recently installed windows seven pro on which I made an admin account, and then my regular account I use for everyday's use.

My issue is that my other partitions contains plenty of data coming from my previous Xp Pro install, and while my admin account can do whatever the hell it wants with it this is not the case with my standard account (UAC pops up everytime I want to edit/move/delete them).

The files/dirs are all owned by an unrecognized GUID (I guess this is my old xp user account).

I tried to use

Z:
TAKEOWN /F * /R

But while it gave me ownership over the files at Z:*, I still don't have "full control" over them granted to me when I have a look at their Effective Permissions.

So then I tried

cacls * /E /G MyAccount:F

But it doesn't seem to work recursively at all.

How can I give myself full control over every single file on drive Z ?

Thanks for any help

PS: I fully understand the risk of that and why user file have specific permissions ect … The drives I am talking about are to be shared. For exemple, the partition containing my music files is affected.