Please note, all - those prices are in Australian dollars' Straight US conversions are $774, $697 and $619. That's strictly applying the current rate of exchange; as those Down Under are fond (not really) of noting, US prices tend to be less than "at home" prices.
Well, the D40 hasn't come out yet, IIRC - it's supposed to come out in another month, and then you'll need to see if there are any "teething pains". The Pentax will have a full warranty, and it's been around for a bit, so should be debugged by now, but take a gander at available lenses (not saying this will be a problem; I just don't know) to see how much growth potential you'll have there. If you don't mind buying used (no warranty), you migth want to consider a 350D or 10D and foregoing the 55-200. The 10D won't take EF-S lenses, but shouldn't be markedly more expensive than a 300D, and has a slightly better feature set. There may be some 350Ds going (even new) for reduced prices since the 400D has been released; that's also worth looking for.