post up a picture of them and it will help everyone to diagnose the issue they are having.

Eric

Maters grow 10 times faster than peppers. They will smother your peppers if they are too close together. Did you start them in the shade or have they hardened off properly? Lots of questions. More info more better.

I suspect they were not hardened properly. You have to slowly introduce peppers to the sunshine and wind. Maybe an hour the first day, two hours the second and so on. If you just stick them into the ground, they will sunburn and die. Not all nurseries harden their plants, so it is cheap insurance to do it yourself once you get them home.

Hmmmm. Usually plants sold by a nursery are hardened off, especially considering that they normally sit in the sun all day long at the nursery.
doups3 how often are you watering them?
How much water are they getting?
Are you fertilizing them?

Rudy

I planted some pepper plants too close to tomatoes last year. The tomatoes definetly grow faster and more aggresively then peppers. And yes the tomato plants will block out the sun like Persian archers attacking the 300 Spartan defenders.

As far as the tomato/pepper issue goes, the above are quite right about how most Tomato plants grow much faster and bigger than Pepper plants and will crowd out peppers if planted too close. But, you are correct in that they are very similar plants in many ways. Generally they are similar in nutrient requirements, pollination process, sun requirements, water requirements and so forth.