If you like, you can use the JDBC-ODBC bridge, which isn't really production quality. But it is free, and sufficient for 'playing around'.
Another free driver is the FreeTDS driver (http://www.freetds.org
). But I wouldn't recommend these drivers. I have recently tried the latest, and had all sorts of problems/bugs. The driver also is not a complete implementation of the JDBC spec. Lots of methods are still missing.
The best commercially available drivers that I know of are the ones located at http://www.inetsoftware.de
. I have found these to be fast... and to work very well.
WebLogic also has drivers, but I've not heard good things about those, either.
As always, try all of them out, and come to your own conclusions. Good luck!