Depends where you live - these trees don't tolerate temperatures below freezing, so in places like the UK, they have to be grown as house or conservatory plants, but can be stood outside during summer. How long you could keep it going in a pot I'm not sure, but some instructions in the link below - scroll down to the container planting section:

http://www.ehow.co.uk/how_5006399_grow-neem-tree.html

You might be able to bonsai it, but then the leaves would be small too. You could grow a young one in a pot but you would probably have to replace it when it got too big for the amount of room and compost you can give it.