It looks like macs are not capable of the new networking protocol used by Windows Vista (smb/cifs). To get them to talk to each other, you will need to downgrade the vista machine to use the old protocol. Here's how to do it:
1) On the vista machine, click Start and type regedit
2) Navigate to \HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\
3) Change the property lmcompatibilitylevel from 3 to 1
You should now be able to connect from your mac to the vista box. Enjoy!