It seems that there is a compatibility problem between the version of Samba, the Windows networking layer built into OSX, installed in Mac OSX Leopard/10.5 and what most NAS (network attached storage) drives use.
I discovered this when trying to get my brand new Mapower MAP-KC31N NAS enclosure to work with it - the drive works fine with Windows, and my Mac can get to the Windows machine, but the Mac cannot connect to the KC31N. The KC31N itself is based on the the "Landisk" controller, which is used in a whole range of inexpensive NAS drives and generally seems to work well, and were it not for the fact that I'm hooking it to a Mac I'd be none the wiser.
Looking around further I've discovered that not only is the KC31N incompatible, but a while range of other NAS drives, including more well known brands - Iomega, DLink, etc, that do not use the Landisck adapter. With all of this I'm inclined to think it's an incompatibility stemming from the version/configuration of Samba itself and therefore something they need to fix.
So come on Apple, please fix this bug so us customers can get back to their work. How's about it?