If you've got the two working together, set your Cubase left and right locators to the length of the entire track plus a few extra (4 or so) bars. Mute everything apart from the Reason parts that you want to record. Go to File/Export/Audio mixdown.
Ensure it's set to wav, 44.100khz, 16bit, stereo interleaved. Give it a filename, and hit save. Cubase will render the Reason parts as an audio file in the location you've set. Re-import the audio file, turn off Reason. Sorted.
Incidently, try
http://forum.cubase.net/phpbb2/
Hope it's a legal copy of both programs though else you'll get banned.