Thats down to Windows security!
It wont let someone who doesnt have the adequate access writes to access the Documents and Settings folder of someone they shouldnty be trying to!
because your hard disks are dual boot, and not the same installation, Windows on the non-boot disk wont allow the currently logged in account to access it.
There will be ways around this using sharing and windows security/NTFS permissions, but would need to mess around with it to be sure. Its easy enough on networked PCs...I've never tried it on a dual boot PC with separate installations before!