I had the same problem in iTunes 7.5. There were two games in my shopping cart that I could neither purchase nor delete (the button that normally says "Buy
Item" said "Veiw
Item"). When I clicked "View" I received a message that said the item was not available in the iTunes Store. And when I clicked the X to delete them, the shopping cart would simply reload, but the items were still there. So to purchase the items I switched to 1-click shopping and bought them directly from the iTunes store. But of course, when I switched back to Shopping Cart they were still there.
I have been trying to delete them for at least a couple weeks now. And then yesterday, I tried again and they were deleted just like any other item would be deleted. So I don't know if iTunes did something to correct this problem, but it's fixed for me! Hopefully you'll find it to be fixed as well.