Windows 7 with all Service Packs and updates takes around 20GB. So you should have around 35.7GB of free space if you installed no other software besides Windows.
Windows updates have to be on your C: drive only.
Run Windows Disk Cleanup and see if there are there any temporary files that you can delete.
You can also go into Control Panel and click on "Uninstall a program". There you will see all programs installed on your system.
Also check to see how many system restore files you have. You can delete any of them with CCleaner. If you have a backup program running check to make sure it's not being backed up on the same drive (although some kind of warning should pop up for that).