When did everyone start working out after giving birth? I am not even really sure HOW I'm going to work out. I really need to be in a gym and I am really going to need to do weights. But, I'll figure something out. So, when is a good time to get my butt back into gear? After four kids, my body is going to need all the help it can get!

I think that having a routine you can do in/around home is key to a consistent exercise routine. So, whether that be getting a treadmill, stair climber, taking walks, using hand weights or an exercise video, you will probably be more likely to actually do some working out if it is easy with a capital E!
Regarding how soon after, I usually don't feel motivated until 8 or 9 mo after, but that's probably too long to wait. I've heard of some ladies starting at 2 mo post birth, which seems pretty reasonable to me, barring any major situations/problems.