We have
posted the source code  for Data
Loader 10 on SourceForge,net, in both CVS format and in a ZIP file distribution.
This new posting is a significant advance over the version of Data Loader
previously available at SourceForge 18 months ago, and
includes a custom web service stack built for high performance salesforce
interactions.  You can freely download this Java application to extend
the functionality of Data Loader, or just to see a good example of how we use
the Apex API to move large amounts of data in and out of the salesforce
database.  As with any open source software, you can
redistribute this code, but please keep in mind that we only support the
existing version of Data Loader, not any modified or extended versions based on
the open source code.