That is a TRULY USEFUL tip. Thank you SO MUCH.

I was using Vista Ult64 and trying to connect to my 10.4 Mac. ("Why upgrade?" :) )

You do indeed have to do exactly this:

“Click Windows Visa Start Orb In search box, type “regeditâ€ and return Once regedit opens, click File -> export to make a backup copy Navigate to Computer HKEYLOCALMACHINE SYSTEM CurrentControlSet Control Lsa. In the right pane, right-click the “LmCompatibilityLevelâ€ key and select “modifyâ€ Change the value from 3 to 1 Exit regedit and you should now be able to properly authenticate to your Mac OS X (or other Samba) share.â€

thank you SO MUCH !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!