Access to files on server

I'm just appalled by the problem I'm having when opening files on our local Microsoft server. Powerpoint files will open, and when saved will complain of a file access error. If I decline to save, and look at the file in the Finder it's been set to zero bytes size, and there is no content - effectively it's been wiped. I know that the permissions are fine on the server, and are reported fine both by the Finder and via the command line.<br>
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I'm using fully up to date Leopard on an iMac (10.5.2), and Office 2008.<br>
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Bill Brocklesby