Merck and Company said Tuesday it has been building sales of key products and launching new products since acquiring Schering Plough in November, and the merger is very much on track. In a briefing for business analysts, Chief Executive Richard Clark said the company is well positioned to meet medical needs, launch new products and maximize shareholder return.  Four new drugs are now awaiting approval and more than 20 others are in the late stages of testing, including several for treating cardiovascular disease.