dont know if anyones tried using kettlebells as an alternative cardio exercise,but its great for HIIT or tabata type cardio,doing kettlebell swings really gets your heartbeat going,here are some sample exercises there are plenty of others.

YouTube - Steve Cotter - Extreme Kettlebell Workout - Kettlebells DVD

You can do anything for cardiovascular conditioning as long as it elevates your heart rate to at least 70% of max heart rate (75 - 85 is better) and you can maintain it for at least 20 minutes, preferably 30. The problem is, unless you use big muscle groups (e.g., legs - running and cycling or back and arms - swimming), the smaller muscle groups wear out long before you get the cardiovascular benefits.