After installing Windows Vista, I could not connect to my Samba fileshares. I'm running Samba v3.0.10 on CentOS v4.4.
It turns out that NTLMv2, the authentication protocol, is required by default on Windows Vista. According to the Samba Features by Release wiki page, support for NTLMv2 in Samba wasn't fully developed until Samba v3.0.21.
Running yum would be a quick way to upgrade Samba to a more recent release. For some reason, though, the repositories I'm pointing to only have v3.0.10 as the latest available update. Rather than hassling with it, I found an article that attacks the issue from the Vista end.
The article Get Vista and Samba to Work explains how to get Vista to use the older authentication protocols, like the original NTLM. After making this change, I was able to login to my shares immediately.
Basically, all you need to do is run the Local Security Policies console snapin (secpol.msc), open Local Policies --> Security Options --> Network Security: LAN Manager authentication level, and change the setting from "NTLMv2 responses only" to one of the more lenient settings, like "LM and NTLM – use NTLMV2 session security if negotiated".
This works for me because I have one, sometimes two, machines with Windows Vista connecting to my server. If you had lots of machines connecting to the server, it'd obviously be worth your time to just upgrade Samba to a version that supports NTLMv2.