This was frustrating me for ages in the end my mate Alan showed me how to do it. Thought I might blog it encase someone else has the same problem.
To insert a check box in 2010 you need to enable developer tools like you did in 2007, its just in a different place.
Go to the document information screen.
Click Customize Ribbon then tick the Developer tickbox.
There will now be a developer tab where you can add the checkbox: