Is Radeon HD 5770 ok with 450w psu?

I'd suggest you get atleast a 600w PSU. While the 5770 is rated at 350w, if you use a quadcore 75w CPU, and the graphics card at full, you're dangerously close to messing up your computer. And that's not counting fans, HD's, or other components. You should always go bigger on the PSU.