I've started Sitecore MySQL provider - to make Sitecore run on my sql database. The first part naturally is to convert existing Sitecore MS SQL databases to MySQL ones. They've been developing 5.0 version for 3 years now and just released the Release Candidate.. but as much as I'd like to do it 5.0 only, we still need to support stable 4.1 versions, so - no stored procedures and no views. I think we will have the 5.0 enabled version in future and I'll try to make the transition as easy as possible, but for now getting Sitecore run on 4.1 is definitely a priority.

MySQL has the MySQL migration toolkit that helps to convert existing databases, and it does support MS SQL. So sure, I've decided to try it first. However it wouldn't connect to my local MSDE server, giving me the "Network error IOException: Connection refused: connect". So I've started writing a error report to mysql forums while banging my head on the wall, and here's the results:

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I'm having exactly the same problem: "Network error IOException: Connection refused: connect" both on the source database selection screen (clicking the [...]) and connecting to servers screen in MySQL migration toolkit.

I have MSDE 2000 installed locally on my machine, so I'm quite positive that host names (I've tried any possible combination), port, user name and password are correct. I can connect to the server using the enterprise manager, query analyzer or whatever else with the same credentials.

I've also ensured that both named pipes and tcp/ip are enabled. This post suggests that MS SQL SP3a helps: I've installed SP4 but again with no luck.

I'm resorting to manual migration at the moment, but I'd really appreciate if I could get migration toolkit working.

Update:
I've searched the web, and tried using named pipes instead of the tcp/ip: jdbc:jtds:sqlserver://127.0.0.1;user=user;password=password;namedPipe=true.

First it gave me some error code instead of the 'connection refused' error and then the migration toolkit application crashed. But it actually worked after restart!

Hope this helps.
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I'm proceeding with the migration at the moment, hopefully more info will follow.