Weird thing with GPU power reqs...
A mate was about to drop £70 on a GTS450 (to upgrade from a 5670) - the psu requirement is a 400W with a single power connector and he has a decent 460W with 1 power connector.
I noticed a VERY cheap 7770 in our local PC World today tho - less than £70 for a MUCH MUCH better card. Problem is the box (and AMD website) says it needs a 500W 'certified' power supply.
Digging around, the 7770 draws LESS power than a GTS 450 - every single test shows it uses less overall and has a lower TDP (or whatever it is) draw
So - erm - is the 7770 worth a try or is the GTS450 likely to need more than it says or - erm...???
No budget left for a decent new PSU atm...