I've talked yesterday about the fact that Microsoft Dynamics NAV 4.x is not officially supported on Windows Vista, and I've said also that I've see tricks in order to run it with the new OS.
First, I've to be more precise: the Dynamics NAV client works correctly on Vista, there's no problem to install and use it.
However, there's a problem when you try to connect to a SQL Server database due to a wrong MDAC detection.
The cause of this problem is the unified versioning of all DLL that Vista has. My friend Kine has found a trick that I want to share with you (reported here in order to don't loose it, it can be useful in future):
As he explain, Navision is detecting MDAC version through File version of SQL ODBC driver (sqlsrv32.dll). On Windows XP you can see version like 2000.85.1117.0 etc, but on Vista the file has version 6.0.5600.16384 and this is “less" than the requested version. Changing MDAC detection in Navision is no way.
The trick to run Dynamics NAV 4.x on Vista is this:
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You need some resource editor tool, for example the Resource Hacker application
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Copy the file sqlsrv32.dll from your Vista system32 folder to another place.
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Open this copy in the resource editor
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Change FILEVERSION value to new value e.g. 2000.85.1117.0 (in the header of Version info ressource)
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Compile the resource
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Save the file (backup original file!)
Now you need to copy the file back into system32 folder. But under Vista, this is not easy task. The file cannot be changed because just installer has enough rights.
Replacing original file with modified one:
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Open properties of the original file
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On the Security tab click Advanced
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On the Owner tab click Edit
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Select new owner of the file, for example your account
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Commit all changes
- Change permissions for your account to have all rights
- Commit all changes
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Now you are able to delete the file – delete it
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Copy the modified file into system32 folder
Thanks a lot Kine... 
I hope that this problem with MDAC will be solved with the next Service Pack releases for Dynamics NAV (SP3 is attended in a near future but there's no sign for this problem).