It's not because you're not Administrator (which you're not - there's a big difference between an Administrator-level account, and the
Administrator account.) Rather, it's because you don't 'own' the folder (and, with it, the folders & files within) - your account in the old Windows install owns it.
While the username might be the same, the SID is not (that's tied to the install.)
Easy fix, though: you need simply take ownership of the folder (and, be sure to tick the box that says 'replace owner on subcontainers & objects.) Then you can grant yourself Full Control on it (here, tick the box to replace permissions on child entries), and copy your data out.
(written for XP; but, does apply to any NT-based Windows OS, including Win7.)