A. As a rule of thumb :-
Microsoft provide support for at least the current and previous version of a product (service-packs don't count). So with 6.5 and 7.0 out Microsoft will actively support 6.5 until the next version of SQL comes out - active means fixing the code and issuing servicepacks and hotfixes. The next version - SQL 2000 (Shiloh) - is due by the end of 1H 2000.
After that Microsoft continue to provide support for as long as they feel the customer base warrants it. This is weighed up against the fact that Microsoft support doesn't make the company any money and they do want to encourage users to upgrade (because that does make them money). For 6.5 I would expect this to be a fairly long period given the installed-base of 6.5. During this time the likelihood of servicepacks substantially decreases but for major problems or major customers you will at least get hot-fixes written.
Once this period finishes Microsoft finishes "active" support. The source-code is still available to the PSS support people for debugging, but no more fixes will be written. Microsoft will still take a support call and help out with a problem - be it performance, corruption etc. They will help you fix the problem yourself or provide workarounds, but they will not fix the 6.5 codebase. If a bug is found they will test it against the latest version of SQL Server and fix it in that if necessary, but your only option to get the fix would be to upgrade.
The other thing to note is that normal staff turn-over, promotions, moves etc. means that the Microsoft SQL support group's experience and knowledge will naturally migrate to the newer/current versions. Staying current with SQL versions/servicepacks is the best way to ensure the highest quality of support.
Microsoft are not actively support SQL 6.0 or below.
Applies to SQL Server versions : 6.5
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