If it's just for Windows, and you can afford it, a 64GB SSD would do you quite nicely. About £95 on here.
If you're just after a standard SATA drive, you may as well get a 500GB or 1TB drive - £33 - £40-ish, because a 160GB is £30 anyway. You don't need the space yet, but if you partition it, it could be useful for backing things up and you can still have Windows on its own partition.