Quite different from iOS 4, iOS 3.2 does not yet support calendars with your Gmail account. Instead, you need to set up a CalDAV account.
To do this on the iPad, open Settings > Mail, Contacts, Calendars and tap on Add Account…, then select Other and choose Add CalDAV Account from the list of choices under the Calendars list.
Next, enter www.google.com as the Server, and use your Google Account Information for the User Name and Password fields. At this point if you exit Settings and open the Calendar, you will find that only one calendar is accessible: your default Google Calendar.
Now, when I open the native Calendar App on iPad, I can see all of my Google Calendars. I’ve added entries, and they’ve all synced nicely. In our household, we have a master Family Calendar on the iPad that everyone can update from a central place. We then subscribe to each published calendar from our personal devices. For family occasions, school events and other shared activities, this is a convenient way to share information with the whole family and still have one central point of control that all can access and update.