Can you explain a bit how you want to use Activiti? You can for example embed the Activiti Engine in your own application and define a MySQL datasource and you're good to go. For more information you can read the Activiti in Action book for all the background and details of Activiti.
Sorry for the late reply. Thanks for the pointers.
We want to know if/how we use Activiti with exisitng Tomcat & MySQL that we have in place. We first want to use it internally, for dealing with complaints workflow that is currently manual.