Just a note in case anyone else runs into this problem.
If you want to connect to a share on a Buffalo Terastation (which seems to be using Samba) from a Windows Vista installation, you need to do the following:

  • Run the Local Security Policy app – secpol.msc
  • Go to Local Policies | Security Options and choose the “Network Security: LAN Manager Authentican Level” item
  • Set it to “Send LM & NLTM, use NTMLv2 session if negotiated”

And that should sort you out.
[Update]
For those of us unlucky enough to be running Vista Home (which doesn’t come with secpol), you can do the following (thanks to Patrick in the comments for this)

  • Run regedit (Windows-R, ‘regedit’) to open the registry editor
  • Find key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\
  • Change the value for the option “LMCompatibilityLevel” from 3 to 1.

Now you should be able to access the TeraStation (you may need to reboot)

[Update 25th August 2009]. A couple of commenters have been kind enough to say that this also works in Windows 7 RC and thus in Windows 7 RTM (pretty safe assumption). For what it’s worth, I have a Windows 7 RC virtual machine running and I’ve been able to connect fine without needing to make any changes that I can remember.