1. Install Db Migrations as a regular Magento Module. It will extend the Mage_Core_Model_Resource_Setup class

2. Configure your own custom module to use Db Migrations. See for instance the following example config

<config>
    <modules>
        <Foo_Bar>
            <version>0.1.0</version>
        </Foo_Bar>
    </modules>
    <global>
        <models>
	    <foo_bar>
  		<class>Foo_Bar_Model</class>
            </foo_bar>
        </models>
        <resources>
            <foo_bar_setup>
                <setup>
                    <module>Foo_Bar</module>
                    <class>Db_Migrations_Model_Resource_Setup</class>
                </setup>
            </foo_bar_setup>
        </resources>    
    </global>
</config>


3. The Magento core functionality only supported installer & upgrade scripts.
Foo/Bar/sql/foo_bar_setup/mysql4-install-0.1.0.php
Foo/Bar/sql/foo_bar_setup/mysql4-upgrade-0.1.0-0.1.1.php

Now you can create your rollback scripts as well.

Foo/Bar/sql/foo_bar_setup/mysql4-rollback-0.1.1-0.1.0.php

4. It's time to play with your custom module's node <version> & the core_resource table and see it working!

Please let me know if you find any bugs/issues.