Yes.  ArcGIS 9.3 can be integrated with Google Maps, Google Earth and Microsoft Virtual Earth in the following ways:

ArcGIS API for JavaScript Extensions
At 9.3, the new ArcGIS API for JavaScript includes two extensions, one for Google Maps and the other for Microsoft Virtual Earth. These API extensions allow Web developers to easily integrate ArcGIS Server map, image, data, and geoprocessing services with Google Maps and Microsoft Virtual Earth applications. Essentially, your GIS data and analytical tasks can be combined with the basemaps and application functionality provided by Google Maps and Microsoft Virtual Earth – creating a GIS mashup. You can learn more about the ArcGIS API for JavaScript extension to the Google Maps API and the ArcGIS API for JavaScript extension to Microsoft Virtual Earth at the ArcGIS Server Resource Center.

KML
Whenever you create a map, image, data or geoprocessing service with ArcGIS Server 9.3, a Keyhole Markup Language (KML) service is generated. KML is an XML-based file format used to represent geographic features in applications such as Google Earth, ArcGIS Explorer, and ArcGlobe. KML allows you to draw points, lines, and polygons on maps and globes and share them with others. ArcGIS Desktop 9.3 also offers two new tools (Map To KML and Layer To KML) that allow you to generate static KML documents that you can e-mail or place on a file server.

Services Directory
ArcGIS Server 9.3 uses representational state transfer (REST) to expose information about your services through a series of endpoints, or URLs. At 9.3, ArcGIS Server provides the Services Directory, which is like a catalog of all the services on your local GIS server. When a user publishes any map service with ArcGIS Server 9.3, a Services Directory Web page is automatically created.  The Services Directory page and all of its map service and KML service links can be crawled and indexed by any search engine.  For example, you can access the ArcGIS Services Directory root page.  These are our public map services powered by ArcGIS Server.

ArcGIS Online
ESRI has worked closely with a variety of data vendors including i-cubed, Microsoft, NAVTEQ, Tele Atlas, and others to offer "subscription services" to our users through ArcGIS Online.  As a result, ArcGIS Online offers a variety of premium services available for an annual subscription fee.  For example, ArcGIS Desktop users will be able to subscribe to Microsoft's Virtual Earth content for $200 per user per year.  This service includes imagery and other basemaps worldwide.  Users can easily subscribe to these premium ArcGIS Online Services online, through the ESRI Store.