Meh, you have no reason to worry about overheating, unless the temperature case is something like 70 degrees don't worry. Anyways is this power supply going to be top mounted or on the bottom drawing cool air from the floor? I believe Top Mount power supplies take the warm case air and exhaust it through the back. Bottom mount facing down to the ground draws air from outside (below the case) and exhausts it the same way.
Either way I believe the capacitors in this power supply to be rated @ 105 degrees which is the standard for quality power supplies.
Anyways according to this review they were able to draw around 550 watts @ full load which is pretty impressive.http://www.hardwaresecrets.com/article/Antec-VP450-Power-Supply-Review/1487/9
Edit: Since you live in Australia, do you know any websites that you use for computer parts? I can look of there, I checked the VP-450 in the australian part of ebay and boy, the computer parts are all overpriced....
They're selling the VP-450 for around $65-70 AU, thats roughly about $70 in CDN, or USD if you want.