Put the GTX 750Ti in this slot-
PCI Express x16 (Gen 2.0) (PCI-E is backwards compatible so 3.0 is not required for that card, it can run on PCI-E 2.0 slots also)
With a power supply get this -
EVGA 500B - You always want watt headroom for the future, to prevent upgrading again. Higher wattage of this type is more efficient also.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...