You should get a tax form in April, which you have to return within a few weeks. You will then get a tax demand (around July-September) which will cover the tax for the period July 2005-March 2006 and provisional tax for the period April 2006-March 2007 (i.e. about 1.75 year's tax). You will need to pay 75% of this in January 2007 and 25% in April 2007.
The legal responsibility is on you as an individual, and the tax office will write to you individually (although they may do so at your company address if they don't have your home address). The most you will pay is 16.5% for something like $50,000/month. Nothing if you earn less than about HK$9,000 per month. There's a scale in between. Thereis lots of information here:
http://www.ird.gov.hk/eng/tax/ind.htm including an indicative tax calculator here:
http://www.ird.gov.hk/eng/ese/st_com..._06/stcfrm.htm