Pretty easy. Follow these instructions: http://www.lta.gov.sg/motoring_matters/motoring_guide_nonwest_regis.htm
What I did the Day after I arrived, and the day before the bike arrived is:
Take all the documentation mentioned in the above link to Singapore AA. and get:
Insurance: They will issue you "Carnet Insurance" which they can only sell for 30 days now, so a minimum of $310. You might be able to shop around if you have more time, but I only had a day to sort the documentation out.
ICP: This little slip of paper cost me $53.50. I'm unclear if this was related to the number of days I was staying in Singapore. Anyway, you must remove the vehicle from Singapore before this expires. They clearly were not too familar with this step as I'm not sure that it had been filled in correctly.
Carnet Endorsement: They stamp the back of the Import slip stating that they are liable for the duty on the vehicle if it does not leave Singapore in 12 months. However, I'm not sure why as this is what the Carnet document itself is for. When you leave Singapore you must get the Export slip endorsed also.
Expect Singapore AA to take about 2 hours.
After Singapore AA is complete, head over to the LTA to get your autopass card. Just hand them all the documentation and they will issue you the card. The whole process takes about 15 minutes, and the card costs $10. You don't need an IU for a car but they will try to get you to hire one, however foreign vehicles are charged $5 for a full day of ERP use if they pass though one (I'm unclear on the rules for a motorbike in regards to the IU, I'll find out at the boarder I guess).
As my bike was Airfreight it was a pretty easy process at the airport. You MUST have your Bill of Lading to gain access to the cargo area of the airport. Make sure you can get a copy faxed to you somewhere. Once you get to the airport you need to surrender your passport to the security office and they will issue you a visitors pass. After that retrieve the bike from the cargo company (addresses will be given to you), reassemble if required, and then ride it out to Customs (stay left!). Customs will go over the Carnet and sign it off. In my case they didn't even leave the office to inspect the bike or ask for the ICP or insurance, it was all done and signed quickly (and with the involvement of around 4 of them), And then you're on your way again! Just remember to stop at security to get your passport back.