In our last episode of enabling new modules via update.php, Steve McKenzie pointed me to a better method: module_enable(). A quick test found, however, that it didn't run the install files, and didn't rebuild the module files cache. So after spending 5 minutes in system.module, I found all the missing pieces. The example update function below will install and enable the new module, as well as rebuild all the css, node type, and menu caches.