Here are the instructions on how to uninstall Process Manager

Login to the database and remove any tables that have pm_ - for example pm_process_completed_process

Updated - 5-16-2011
Customer called and ask to update with more explicit instructions:
Login to your favorite mysql admin tool like phpMyAdmin.
Open up your sugar database and remove all tables that have pm_ in their name - there will be quite a few.
Delete these from the database. Then follow the next instructions below:

If not already removed by unistall process:
- remove /modules/PM_ProcessManager
- remove /modules/PM_ProcessManagerStage
- remove /modules/PM_ProcessManagerStageTask

Remove zip files in /cache/upload/PM_CE_60_MYSQL_V2.zip - or the name of the PM file you uploaded

Check the folder /cache/uploads/upgrade/module - remove any Process Manager files

Now run the following sql select * from upgrade_history
Delete any entries in this table for PM

Check the db table tasks - if the column is_pm_created_task is present - delete it

Check the db table upgrade_history - you will see an entry for Process Manager - delete it

Run quick repair and rebuild