Yes, you ned two trees to get fruit.

Ok do they have to be different varieties

Planting from seed will mean they are in effect different varieties I suppose so you are good. There are some neat varieties though... I would recommend this guy http://www.nuttrees.net/ if you decide you want more variety in the seeds you plant. His operation is near me in Kentucky and can provide different types of seeds if you decide to go that route or seedlings or grafted varieties at a very reasonable cost.

I've just planted about 20 or so this year but beyond the planting don't have experience with them yet myself.

Hi Andrew, HERE is my lengthy thread on pawpaw. I've been growing seedlings for many years. I grow the seedlings mostly for wildlife habitat. As the others have said the grafted ones make superior fruit. It is worth noting that even with the grafted ones you still have to start with a seedling for understock.

If one really gets desperate for pollination try this: at bloom time get a few blooming branches from a different tree, put them in a bucket of water and put beside your tree, see if that works.