Every year a maximum claimable GST amount is set by the ATO on motor vehicles. This year the amount is$5,198.00

Car Limits 2009/10

The car limit for the 2009–10 financial year is $57,180. This limit is reviewed each financial year and may change.

The fuel efficient car limit is $75,000 for the 2009-10 financial year. A fuel efficient car is a car that has a fuel consumption not exceeding 7 litres per 100 kilometres. Luxury car tax does not apply to fuel efficient cars under the fuel efficient car limit.

Generally, if you purchase a car and the price is more than the car limit, the maximum amount of GST credit you can claim is one-eleventh of that limit. For 2009-10, the maximum GST credit you can claim is $5,198 (that is, 1/11 x $57,180). This limit also applies to cars which are fuel efficient.

If you purchase a car with a price that is more than the car limit, you include only the amount of the car limit (or the proportion of the car limit relating to business use) at G10.

source http://www.ato.gov.au/businesses/content.asp?doc=/content/18276.htm&page=4&H4