Palin could come in in February and win.
Sarah Palin said she’d announce by the end of September, so let’s just take her at word and leave it at that. She knows she can’t announce any later than that and participate in the critical IA caucus or NH/SC primaries.
But, no, neither she nor anyone else could come in in February and win. That would be too late to enter the early caucuses/primaries. By the end of February/early March, GOP primary voters will coalesce around one or possibly two candidates. I’d venture it will be all but over by the first week of March, 2012.
The purpose of primaries and caucuses is for the candidates to line up delegates to the nominating convention. As they are selected, they will be committed to whichever candidate they were with in the primary.