This works only when the filesystem is supported by MacOSX. I've been trying to access my files on a ext2 filesystem, which isn't really supported under MacOSX. One reason to buy Parallels for me was being able to do that. Unfortunately the evaluation went by too quickly and I didn't test this. It's a shame, because it's very likely to be comparably easy fixed.
Well... I bought it and it doesn't work. Same applies to other needed features (see http://forum.parallels.com/showthread.php?t=21094).
I replied in http://forum.parallels.com/showthread.php?p=107921#post107921, as this the the relevant thread.
Ok, can see, I will try to reproduce. meanwhile, try to run Parallels Transporter for Linux http://www.parallels.com/en/download/file/v3/en/GA/Parallels-tsp-3.0.1456-lin.run and run in place migration (to external attached HDD)