Wille-o. I think you need to be a little careful. I know some ATX cases have mountings to take a Mircro ATX motherboard but I'm not convinced they all have.

McGrath seems to have made it clear that he doesn't want to replace the case but it would be my route together with a higher wattage power supply. Rather than spending on a Micro ATX power supply, for an extra £10-15 you could probably get something which would allow a much greater range of upgrades in the future.