I was wondering about the status of that awesome 5850 card, hope its all going well. Btw I am not in such of a hurry... you know, take all the time you can mister!
I wouldnt recommend it since ATi says a minimum 500w PSU is required. From the official website: 500 Watt or greater power supply with two 75W 6-pin PCI Express® power connectors recommended.
Putting one on a 460w PSU would be a big risk. Get a bigger PSU and if possible, something better than a CM ExtremePower PSU