Q: I just updated to Windows 7 and Itunes won't let me add my laptop to the as I have too many devices.  But it is that same device just differnt working sytem?

If you mean computers that are authorised (iOS devices aren't authorised/deauthorised) then you can't see a list of which computers are authorised, you can only see how many : http://support.apple.com/kb/HT1420

For devices/computers that are associated to your account you can see a list of them, and if it's been more than 90 days since a computer/device was associated remove the association, by logging into your account via the Store > View Account menu option on your computer's iTunes : http://support.apple.com/kb/HT4627