Wow, you need a lot of work there man! If you cannot complete one abdominal curl then you really need to start busting your ass to get in shape my friend! This pain is just the burn you feel in your abdominals when you work them. It takes most people a few sets to feel this burn, but you're a little out of shape. You need to conccentrate on things other than abdominal curls and crunches right now. Just because you have a gut doesn't mean that you work your stomache to death, because that won't work at all. I don't think you are listening to the information that everyone is trying to give you here. YOU CANNOT SPOT REDUCE! That means that you cannot pick the area you wish to lose fat from. You need to focus on your diet, which means eating lots fresh vegetables, a few fresh fruits, lean meats, and very few processed foods. Next, you need to focus on your cardiovascular workout. You need to jog, sprint, bicycle, ect. for 30 minutes a day, 3-4 days a week. Then, you need to start weightlifting. I already posted a workout for you, so you should really concentrate on those lifts and finding someone or something to show you how to perform these lifts. You need to get your total body fat percentage down to get rid of that gut. If you simply do crunches and abdominal work every day you are not going to see ANY results. Actually, your stomache may actually get bigger because you will push that fat further out to the surface. Sadly most people these days are looking for the easy way out. The quick fix for things. They want to sit down and do crunches for an hour and expect to look like a bowflex model. The benefits of a total body workout combined with cardiovascular activity are grandiose. You will have more confidence, feel better, get ill less, have a better self image, and the list goes on. But none of this will come from doing crunches and eating big macs, sorry.
scott