Hey Kate -
MamaJama and I are over in another thread talking about doing short bursts of activity throughout your day - rather than trying to block out 30 or 45 minutes all at once.
I'm used to really vigorous workouts for longer periods of time. But, last year, that was just not in agreement with my schedule.
So, I would get up a little early, do 10 minutes of yoga, walk at lunch, and then play soccer, ball, or hop-scotch with my daughter when she got home from pre-school.
I was a little worried when I started doing that - thinking it wouldn't keep me fit - but it worked like a charm!