Maybe reformat the drive.
Works fine for me. I just tried plugging in a USB stick, sharing it...adding everyone group. Then on the WDTV, I select movies, and Network Shares, select Windows Shares, select my computer's name, click ok and it sees the shares.
The drive I shared was formated as a Fat32 drive, so there were no NTFS permissions to worry about...then again, there are limitations to Fat32. I would format the drive and start from scratch, but if it is loaded full of media, you might not want to do that.
Try doing the same thing with a USB flash drive/USB stick and see if the WDTV sees the share....if it works with a stick but not your hard drive, then the problem is the hard drive/permissions on th drive.