Recently my friend's laptop broke down and he gave me $100 while he was on a holiday to upgrade the GPU on his old Dell Optiplex 745 Desktop form-factor for him. The specs for this system can be found here (He has the Core 2 Duo version):
His system does have the riser option however I am not sure if the card will fit in the case (desktop form-factor) and if the low-profile slot will be too small for the card. He will be using it for about a month for light gaming till he gets his gaming laptop back. If the card is not compatible for one of the reasons above or another one I haven't realised, would you please be able to offer an alternative.
The GT 730 is just a rebranded GT 630. There are only 2 sizes for video cards, full size and low profile and if he has the "desktop" size from the picture you posted then you will have to get a low profile card. The GT 630, GT 640, and GTX750 all come in low profile, are all extremely short, and will work fine with just the power form the pci-e slot. The GT 630 is not going to be too great for games though, unless they are ran at a low resolution or a very low setting. You can get a GT 640 for about $80 or a GTX750 for about $110.