Kevin Rudd is giving a live press conference currently in the US and whilst he hasn’t actually said 100% definitively that he will challenge, it sounds very much like it.
Julia Gilliard will give a press conference in about 20 minutes, when she will announce that she is accepting challenges for her position and this is expected to happen on Monday morning next. (Edit: This press conference has been delayed a bit, no doubt while the Gillard camp soak in the Rudd comments)
Any uncertainty on the political front will probably weigh on the AUD in the short-term.