As the poster before me said, if a food has less than 0.5g of any item listed, it is allowed to say zero trans fat (this gives some slack due to manufacturing process remnants). What this means for you is that food companies have effective hidden trans fats by decreasing the serving size to hide the trans fats. They are then allowed to claim "zero trans fats". So, you are doing the right thing by looking for partially hydrogenated plant oils on the label. It is best to avoid trans fatty acids completly!
Here are a few resources that I have found along my path:
Food Labels -- Nutrition information and misinformation (Page 3 of 3) Trans Fats - What are Trans Fats or Hydrogenated Fats? Revealing Trans Fats Healthy Person: 10 Worst Trans Fat Foods Ban Trans Fats: The Campaign to Ban Partially Hydrogenated Oils Trans Fatty Acids and Coronary Heart Disease, Department of Nutrition, Harvard School of Public Health
Hope that helps and stay healthy!