Yes, they will cross pollinate. Try to plant them far apart or don't use the seed. OR use the seed and see what you get!!!

Here is a link that might be useful: How my garden grows!

It will affect the seeds for following years, but not the fruit this year.

Okay, I went to the source once I had time. The Aggie Horticulture PlantAnswers site says:

3. Q. If you plant hot peppers beside sweet peppers, will the sweet pepper plant produce hot fruit?

A. Absolutely not. Pepper flowers are self-pollinated, although occasionally cross-pollinate. However, the result of this crossing will appear only if seed is saved from this year's crop and planted next year. It will not result in off-flavor or differences in fruit characteristics of this year's crop.

It can produce hot fruit the FOLLOWING year. Anytime the pepper plants cross you will only see results from using the seed. All the fruit will be of what you planted.

You can plant them next to each other but you just have to purchase new seed next year if you don't want anything to cross (I love seeing what crosses personally.)

It's possible for them to cross, but of course that won't affect this year. It would be rare, though. My understanding from our extension is that they nearly always self pollinate.