IE9 is very stupid with gradients so you have 2 options.
1: cut on photoshop 1px from saved .png and use it with repeat-x
2: take a screen shoot and save as gradient image after that convert your gradient background with: http://websemantics.co.uk/online_tools/ ... convertor/.

Off the top of my head I'd check that the htc file is being served with the correct content-type header -- IE9 is particularly strict about that whereas other versions are sometimes more lenient.

Have you inspected the HTTP traffic to see what files IE9 is requesting? To make sure it's loading your conditional stylesheet and the PIE files.

Use a network proxy like Fiddler to inspect the requests it's making. Or perhaps IE9's own built-in developer tools will let you see the network requests and their response headers.