COM+ 1.5 has the ability to run any server application as a NT service, so that the application is up and running when the machine reboots, before any client makes the first requests. This improves the response time of the COM+ application. Besides, running a COM+ app as a service means that it can run under the system account.
You can configure a COM+ application to run as a service by ticking the "Run application as NT Service" checkbox in the Activation tab of the application's Property dialog box. The "Setup new services" button brings up a dialog box where you can configure other properties of the service, such as its activation mode (should use Automatic to leverage the service's potential) and service dependencies.