Lonetrout :
I have a few old pc's a laying around most of them with lga 775 boards and ddr2 what would i have to do to do moderate modern gaming like titanfall. I will probably put a gtx 750ti on this build.
I don't have much experience with DDR2, but given the huge jump in performance between DDR2 and DDR3 which the game is intended to run at, I'd say that the CPU and RAM would probably be a huge bottleneck for the graphics card. If its the old pentium CPUs running on a 775 mobo with DDR2 you're screwed out of the gate. Some of the Q series cards run well though.
If you're going to upgrade on a budget go for a cheap skylake board and an i3 6100. Gives great performance for the money. If you can pay a little more get the i5 6500.