I am trying to upgrade my OptiPlex 745 with Radeon HD 6770 video card.
according to dell website, I got
Will this be good to support Radeon HD 6770 video card?
I also noticed that Optiplex 745 only has PCI-E 1.0 slot, will that work with Radeon HD 6770 video card which is PCI-E 2.x desing too?
No, that card is too big for a mini tower and also, the 300 w PS will not be enough to run that card. you need to find a card that's low profile.
Something like this one: http://www.newegg.com/Product/Product.aspx?Item=N82E16814161374