One of the important thing in configuring Tivoli Common Reporting server is the JDBC configuration. This step doesn't seem to be documented in the installation guide properly. The installation guide talks about modifying a python script but it is not needed and there is a simple way to get configure the JDBC driver.
The simplest way to get it working is to copy the JDBC drivers to a particular directory deep down in the TCR installation tree. The location is %TCR_HOME%\lib\birt-runtime-2_2_1\ReportEngine\plugins\org.eclipse.birt.report.data.oda.jdbc_2.2.1.r22x_v20070919\drivers
Once you copied the JDBC drivers to that location and recycled TCR, the driver classes will be available to TCR and you should be able to configure JDBC connections using TCR web interface (Right click on a report -> Edit Data Sources).
Hope this helps.