http://howtomakeiphoneapps.com/2009/03/how-to-add-a-nice-background-image-to-your-grouped-table-view/

What you need to do is create a view with your background image and add that view to your app’s window. Then you must set the table view’s background color to “clearColor”.

Here is how you would do that from the app delegate:

UIView *backgroundView = [[UIView alloc] initWithFrame: window.frame];
backgroundView.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"TableViewBackground.png"]];
[window addSubview:backgroundView];
[backgroundView release];

yourTableViewController = [[ATableViewController alloc] initWithStyle:UITableViewStyleGrouped];
yourTableViewController.view.backgroundColor = [UIColor clearColor];
[window addSubview:yourTableViewController.view];

[window makeKeyAndVisible];

yourTableViewController is declared at the top level of the app delegate and ATableViewController is a subclass of UITableViewController that simply displays the rows and sections in the example.