When introducing students to rhythm, I explain it in terms of things they already groove to - the natural rhythms they have been experiencing for many years like: walking, running, biking, hopping, breathing, a beating heart.  We all have steady grooves happening.  As with song tempos, some are fast and some are slow - sometimes we walk fast (like a ticket weilding Steve Buck walking towards a venue where Jethro Tull is about to play ), sometimes slow.  Let's say you're walking down the street.  Well, you don't walk down the street with footsteps sounding like you are falling down the stairs - NO!  I mean, you might if you have some bull terrier latched onto your calf; but, generally we've got a nice steady pace when walking.  Same thing with your heartbeat.  Feel your heart's groove.  If it's all erratic, then there are big problems (get to a doctor- FAST! - hope you make it!).  The heart is doing it's beat-thing at a steady pace.  Just like music - if you don't have a solid groove, then there will be some problems.  Dig?
     So, we start walking.  As we are walking, we start assigning a number for each foot: Left = 1; Right = 2; Left = 3; Right = 4.  We begin counting rounds (bars) or four as we walk up the street - or anywhere!  You can teach many rhythmic ideas this way.  for example, when getting the feel of sixteenth notes the steps are Left = "one"; Right = "e"; Left = "and"; Right = "ah."  I like to skip rope, so I generally go through the rhythm I fancy at the time.  It's a great way to feel rhythms.  Of course, when comfortable with the excercise you can count sixteenths as "one, e, and, a" on the first step and try to fit in "two, e, and, a" on the second step - and so on.  I really worked on my quintuplets this way!