Am I missing the point as to what an admin is?

Renaming files anywhere in your user folder should *not* be requesting admin privileges.  Check the permissions on the files; your user should have full control and ownership of the files. ("Replace all child object permissions..." and "Replace owner on all child objects" in the dialog that appears when you press Advanced are helpful here if you have a bunch of files with invalid permissions.)

You copied these files from a different machine, presumably?  Probably via an NTFS formatted external drive?

Was this from inside a shell open or save dialog in IE?  If so, this is expected behavior (as a result of protected mode)--  a protected mode process has fewer rights than even a limited user account, so it can't rename files without elevating.

If it was from Windows Explorer (outside IE), something's messed up permissions on the file you were trying to rename (or on the parent folder).

Duh...  everybody knows it's far easier to visit a website and upload and redownload your images every time you want to make a change than it is to visit a website once and download {Paint.Net | Irfanview | Gimp | Picasa | *}.