There is BETA JDBC driver for MSSQL Server http://msdn.microsoft.com/downloads/sample.asp?url=/msdn-files/027/001/779/msdncompositedoc.xml&frame=true
Sadly only SQL Server 2000 is supported by the JDBC driver. Not much use if you are forced to remain on 6.5 thanks to a product that supports no higher version since the company who makes it went belly-up
Microsoft has free software that's only useful if you upgrade to the latest and "greatest" version of their for-pay product? After the competing company has gone out of business? Wow, who would have seen that coming? What a stunner. Wow.
And if they hadn't produced a JDBC driver for their main database product, I bet someone would have said that was typical MS behaviour in preventing people from using Java on MS systems. They can't win, can they?
We use inet's opta drivers for SqlServer 7: http://www.inetsoftware.de/English/Produkte/OPTA/, and have had no problems. It's not free, but it's actively supported and they release bug fixes at least monthly. We've also used BEA's jDriver: http://www.bea.com/products/weblogic/drivers.shtml, but it didn't play nice with ATG's Portal product: http://www.atg.com/en/products/portalsuite/. Can't remember what the exact issue was.
I have used NewAtlanta's JTurbo driver, but have later migrated to the now released Microsoft driver.
I've had minor problems with the JTurbo driver regarding it's misreporting of null wide character columns.
And the beta version of the MS driver borked at wide character columns greater than about 250 characters long.
The main advantage of the MS driver if you are using 2000 is the fact that it is free (well, you did just pay for the database after all!)