No matter what was said in the past, if you have first filed a patent in Taiwan (Republic of China), within 12-months' time, you want to file the same patent in China, you cannot claim the priority date of the Taiwan application.
Starting from 22 Nov 2010, you can do that (with a small but).
On 12 Sep 2010, China and Taiwan had agreed to accept and recoginize each other's priority certificate. So for a patent application first filed to Taiwan patent office on or after 12 Sep 2010, the same application can be filed to China patent office after 22 Nov 2010 and claim the priority date of the Taiwan application. When filling in the proper forms, it should state that the first filing office is "Taiwan Region", not Republic of China.
It is good to know that, though two patent offices required filing in Chinese, but in Taiwan, you need to file in Traditional Chinese, while in China, you need Simplified Chinese. And apart from character translation, the use of technical terms are different. Some type of redrafting is required between the two versions.