mh, i don't know exactly about thunar and pcmanfm (i don't use any file manager on my machines, always commandline tools) but maybe they require some packages, like 'gvfs' 'fuse-utils' 'gvfs-backends'
also, try starting pcmanfm from the terminal, and see if when you try to access this samba share you get any error in the terminal
you can use the local ip if you're in the same network, but the hostname should also work

another possibility is that pcmanfm was compiled without samba support, even though i somehow doubt that the debian folks would do that, but it's possible. in that case you would have to recompile it by yourself; but first try troubleshooting it using the terminal as described before