When upgrading to XX or newer on MK9 hardware, you'll need to upgrade the memory to at least 2 GB. You can upgrade to the maximum support by the motherboard, but since the game is 32-bit, it won't be able to access more than ~3.6 GB of RAM.
For the CPU, you’ll need to upgrade the CPU to at least Core 2 Duo E6300 (or its modded Xeon equivalent) for smoother experience. This shouldn’t be an issue for G31/G41 chipset but for 945 Express chipset, please check your motherboard’s supported CPU list.