a different ohm question

this is probably another dumb question, but I am looking at getting new subs and a new amp and keep seeing subs that say they operate on 2 or 4 ohms and amps that say they can operate on 1, 2, or 4 ohms. I noticed that on average, the amount of power it can handle (subs) and the amount of power it can put out (amps) doubles from 4 to 2 ohms. My question is if I get an amp and a pair of subs that can run at 2 or 4 ohms will I be able to switch the ohms? Would I have to wire it differently? and would it actually be louder from one to the other? or is it just another trick to make people think that something can be more powerful than it really is?

Subs, or any drivers, can handle only a set, specified amount of power.  Whether they are single coil, dual, or whatever.  That said, the differences in output power are attributed only to amplifiers.  Amps that are rated to the lowest ohm loads have electronics that can handle the higher current they will produce without overheating and letting out the smoke.  But because an amp is rated at 1ohm stereo (same as 2ohm bridged mono), doesn't mean you have to use it that way.  But it does mean that it is more than likely of a higher quality than an amp that does not show those higher output ratings.

For the second question, will you be able to switch?  Let's say you bought a nice amp that is specifically made to drive subs, a mono class D.  You would typically use it at the 2 ohm rating.  The subs would be chosen so that their combined impedence would equal 2 ohms.  For example, two SVC 4 ohm subs, wired together in parallel.  But to switch these to a 4 ohm load?  No, you couldn't rewire the subs to attain that impedence.

But if you had a class A/B 2 channel amp to run the subs, you would find that it (most likely) is rated no lower than a 4 ohm bridged input.  With that amp, you would not choose those subs because you can't get them to a combined 4 ohm load.  So instead, you would go with two 4ohm DVC subs to get the right load.

And, finally, absolutely yes, the lower the impedence the louder it will be.  The amp will produce more power.  So take everything in consideration when you make your decisions.  And match as closely as possible the RMS of the sub to the power output of the amp, at the impedence you have elected to go with.

Two 500 WRMS subs...like the Eclipse Aluminum, for example.  You'll want an amp that pushes 1000 Watts safely at 2 ohms.  An example would be the Hifonics Brutus BX 1500D  http://www.purecaraudio.com/index.asp?PageAction=VIEWPROD&ProdID=2187  Notice on the specs provided here that this amp is rated at 1500 W X 1 at 1 ohm;  1000W X 1 @ 2 ohm;  500W X 1 @ 4 ohm. 

The amp watts will be divided between the number of subs that are hooked up to it.  Use the same reasoning for any combination of amps / subs.  Good luck!