You can shake your seats, windows, floors..... with the right subwoofer trust me
DJD if you are thinking about getting a surround sound system I would avoid most of the Home Theather in a Box systems (HTIB), you know the ones that come with everything in it like the receiver, surround speakers, subwoofer.... and put together your own setup. It will cost a little more but it's well worth it in the long run.
Not saying that some of the HTIB systems don't sound good, just that you can spend a little more and get a lot more performance most of the time.
This place
http://www.avsforum.com/avs-vb/forumdisplay.php?f=88 has more info on home audio speakers, subs, receivers.......... than you could read in a life time. Losts of post about putting together budget based systems that perform very well.