I'd not use a 750ti, they can have legacy bios issues.
You'll need 4Gb of ram. With just 2Gb, you will have issues with any game newer than Call of Duty or original Starwars Battlefront II.
The upgrade depends a lot on the psu, but for most compatability with smaller stock or non pcie psus, the gt740 is about as good as you'll get for a pcie 1.1 board. Stay away from AMD, their newer cards are not compatible with that mobo.