I have the same problem with my Conceptronic CH3HNAS and have found a free and easy solution.
Since a lot of people report they are able to access their NAS using apps other than the Finder itself, I decided to look for a free Lion-compatible File Manager to use instead of Finder.
I have found muCommander ( http://www.mucommander.com/ ) and indeed it works fine. All I did was click on the button highlighted bellow, go to "bonjour services" and select my NAS. It prompted me for my username and password and voilá, it works fine.
I keep Finder for everyday use and just load muCommander when I want to access the NAS. At least now I don't have to start my WinXP VM anymore just to access it.
Hope it helps you.