For American students, you are NOT required to have step 2 CK or CS for the match. You can take both components in May 2012 for all anyone cares. If you WANT your CK scores included to get interviews, you want your scores no later than mid to late October. Depending on specialty and how bad your step 1 score is, you'd want CK even earlier. For CS, most programs that require it will want it before the rank list is due (February 20ish).
If your an IMG/FMG, you'll need the scores to be ECFMG certified. You need to be certified to apply to the match (I think). The closer you submit your application to September 1st, the better.