I'm 5"9' and training for half a marathon as well. When not training, my daily caloric intake is of 2500. When training, and if i want to keep my weight, i have to elevate it to at least 3000 calories to compensate for the extra calorie expenditure. The 2000 calories per day thing is nothing but a number that tries (very badly if i may say) to generalize the caloric needs of ALL people.
If I was going to live on a 2000 calories a day diet, I'd be a skinny mofo i tell you. When running one burns at least 100 calories per mile, so if you're running 30 miles a week, you should be adding about 3000 calories per
week to your diet (about 500 more each day), the easiest way to do it is eating lots of pasta (skip the butter, cream etc... that have high caloric values but is mainly fat), you should not be afraid of adding calories to your diet, is a high calorie intake plus a sedentary life what makes us get fat. When Lance Armstrong was training, he consumed between 6000 to 8000 calories a day, and he had a 2.5% - 4% body fat %.
Check these links:
http://www.runnersworld.com/topic/0,...00-0-0,00.html
http://in.rediff.com/getahead/2005/jan/10marathon.htm