Starwood and Etihad Airways announced their new partnership back in June. They both had dedicated pages and websites up about the ability to earn Etihad miles on Starwood stays and about the transfer option of Starpoints to miles. Unfortunately, the actual functionality was not up at that time.
Now, you can easily transfer Starpoints to Etihad miles. You just need to log into your SPG account and choose the option of transferring points to airline miles.
You can top up your Etihad account so that you can issue an award. For elite SPG Platinum members there is no minimum transfer requirement. I have few times transferred just couple of points to qualify certain partner promotion and/or hit the number of required miles to issue an award.
If you need to transfer more miles, it is best done in the blocks of 20K Starpoints that always get a 5K miles transfer bonus. Your 20K SPG points will turn to 25K Etihad miles.