We're running into a problem with certain files and folders on our Windows 2003 R2 file share. The problem only affects OS X 10.6 clients.
Certain files and folders on the share seem to lose their filetype association. For 10.6 clients, the file or folder becomes greyed out. Older OS X clients (ours here are running 10.4, I don't have a 10.5 machine to test with) and windows machines have no problem.
In addition to becoming greyed out, if it's a folder, the icon displayed in the list view is the generic document icon. (You know, the blank piece of paper with the top-right corner folded down) Quick look and Get info both still indicate the "kind" is folder, but double-clicking the folder does nothing. The folder behaves completely normally in the terminal, only finder has the issue. Renaming, moving, or copying the folder to a local drive does not resolve the issue.
Eventually figured this out. Someone on the team noticed that all the affected folders of files had create dates that were in the 1940s.
It turns out that OS X 10.6.7 doesn't deal very well with files or folders that have invalid create dates. The fix is to use SetFile to set the create date to something sane.
ex: