Windows 7: Who is 'TrustedInstaller'??

Are you doing it from disk management ? I`ve never run into an issue yet formatting a secondary drive with Windows 7.

So,if I understood well,you have a problem accessing your imported files,right?
Basically,if you don't want to use your already saved system image,the most easier thing would be just to add a permission,not to take ownership.
I know,easiest thing right now is to take ownership with one click using registry tweak,but...
If you take ownership,you will probably have problems when installing something,or when your system would need to install something,and then you'll change ownership again,and again,and finally you'll be lost at all that mess.
Believe me,I've done that,I took the ownership not just of single folder but of the whole partition.And what happens?Yes,you acces files that you need at the moment,but later you can forget about doing anything except copy them.You can't write into them,you can't install nothing,so you have to give ownership back to system even if you just want to add something to those folders,because they remain read only,and you can't change it.
So my advice would be not to take ownership but just add a permission,if you don't want to use your backup,like somebody said in the beginning.

Just convert the original owner as you. For eg. The owner is "trusted installer", then you have to change to yourself as a owner (in this case apply this ownership to the entire hard disk) and it will do the needful.