The HD5750 may run but it's risky to push low end PSUs to their limits. I would avoid any card that needs an external power connector on a power supply with 19a so the HD5670 is the best choice without an upgrade.
That sounds like a cheap generic PSU. It may be good for 60%-75% of what's on its label. A HD5750 under load might kill it, and cheap PSUs tend to take other parts with them when they die. I would not risk it. The HD5670 that jyjjy mentioned will be a significant step up from your 8500GT, and should be safe.