I had that problem once in the Public Beta. The problem was that the tcsh shell that terminal was using went missing, along with a bunch of other BSD related files. The fix was to change the shell in Terminal.app's preferences to use one that's not missing (I used zsh) and then copy the...
It sounds like you are indeed trying to access a windows workgroup. I'm not familiar with DSL, but I think that has nothing to do with it - any group of PCs on a LAN (connected via hubs or the like) can be a workgroup and share files, they don't need the uplink that DSL provides.
To share...