Are there any laws against switching the engine on a car?

Yes legally you're only allowed to put an engine in that is the cars year or newer and the engine had to come in that model car.

But how would the police find out?

It has to do with state emissions. Every state is different.

I see,then if it is illegal to put an engine that does not originally come with your car how come so many people on these forums have their engines swaped.Do they just not go to emmissions?

It has to do with state emissions. Every state is different.
Yes, every state has different laws reguarding swaps.The general rules are...same year or newer (96 ITR motor in 94 Si = good, 96 ITR motor in 00 Si = bad), same class (So CRV swaps into hatchbacks are illegal, because they are a light truck), and mechanically identical (no twin turbo rotarys in a Civic). But like I said, depends on where you're at.

Thanx for the info. What good motor would you recommend to swap into a 2002 civic lx.I want to do a swap,but not untill I have enough money, and also what other things do I need to buy when I do the swap.

K20A...mounts, header, wiring harness, more research.