Can't get out to run, using a cross trainer is a great alternative. It's gentle on your limbs while mimicking movement very similiar to running.
However, be caution with a treadmill, it can be quite stressful on your ankles, particularly since we are road runners.
Other options - pull out those exercise DVD's.
Pick up your dumb bells and do a circuit of weighs and some body weight exercises such as push ups, burpees, lunges, squats, step ups...
Take the time to do lots of stretching!!!!!!
