I'm having issues with this too, now, following upgrading my hard drives.
I had everything working OK for months, and then upgrade my hard drives to 1.5TB, and every since then I've had nothing but problems. I've got one PC running Win XP which can access everything on the dns-323, and another one that can't get into one of the directories I created on volume_1, and I can't see any reason why that would be.
If I could just run a terminal shell and issue some chmod and chown commands, I'm sure I could fix this in about 10 seconds, but without that, it's very frustrating.