Bear in mind, filesystems are not Parallels' job
Bear in mind that the host OS has to be able to understand the filesystem on the virtual disk, and if that's NTFS, the code doesn't exist for Mac OS X (to my knowledge) and sorta kinda works on Linux because it's not an open specification.
So if you're using XP and NTFS, which is generally the right configuration to use, you won't be able to read the filesystem any more than you would if it were a real hard disk that you pulled out of a PC and stuck into a Mac. In the case of FAT32 etc. that wouldn't be a problem. Just pointing out that Parallels can possibly provide a way for a Mac to see the data inside a virtual disk but that that's only part of what's needed if you want to be able to access the data therein.