DVD files have ownership of 501 so can't copy

[Lisi]

I have some files from previous installation that I am trying to copy.  The 
ownership of the files is 501 and I am being told that I do not have 
permission.  My attempts to change teh permissions fail.

How can I get at these files?  I am running LinuxMint7, but from an admin 
point of view it is Ubuntu, since it is very much based on it.  LinuxMint7 
is, I think, based on Ubuntu 9.04.

TIA
Lisi