Anyone tell if there's driver for Intel GMA X3100? I installed Elementary OS on an old Mac but it uses an alternative driver and works badly.
There is no "alternative driver" for Intel GPUs. Intel releases their Linux GPU drivers as Free Software and those are installed by default on your system. Your hardware might be simply too outdated to run properly with elementary OS, but "works badly" is unfortunately not really informative concerning the problems you experience.
You can try a later kernel with
sudo apt-get install linux-image-generic-lts-wily
Note that this might break certain peripherals such as WiFi or sound, but booting back into the older kernel and uninstalling should fix any problems. Just make sure you can see grub before trying this.