This study will assess safety and tolerability of metformin plus GSK189075 in people with Type 2 Diabetes. About 48 people will participate in this study. Volunteers will not know if they are receiving GSK189075 or a placebo. Participation will last about 5 weeks including a run-in period of up to 2 weeks if necessary to increase metformin up to 2000mg daily, a 13-day treatment period, and a follow-up visit about 1 week after the treatment period. Volunteers will remain in the research clinic beginning 2 days before they receive the first dose of GSK189075 until after the morning dose on the fourth day and from the afternoon of the 12th day of dosing until the morning after the last dose. They will have clinic visits on dosing Days 6, 8, and 10. Volunteers will be given equipment and instructions for measuring their blood sugar at home and will be asked to keep a study diary. Blood pressure, heart rate, laboratory tests on blood and urine, physical examinations, reports of drug side effects and ECGs will be obtained during the clinic visits to assess safety.