I live in an older house (California) and the overhead light fixture boxes seem small. They unreceptive to the fixtures my wife has purchased from Ikea in that they have two holes for accepting screws and no amount of cajoling the Ikea fixture will cause its holes to line up. I've picked up an adapter plate from a hardware store but none of its holes line up with the fixture's holes either. Am I doing it wrong?
If it's not a standard junction box, you could always replace it with a new one. A standard octagonal junction box should do the trick:
If the old box wasn't located near a ceiling joist, I'd recommend something like the Westinghouse Saf-T-Brace. You don't even need to go into the attic to install it. (You do need to know which way your ceiling joists run though.)