Stick with your current motherboard.
A PCIe 2.0 device is fully backwards compatible with all PCIe 1.x motherboards (and vice verca).
As you are not going to be able to fully saturate the bandwidth of your current PCIe 1.1 16x slot with your chosen GPU anyways, you will have no performance gains in upgrading the motherboard alone.
Wait until you have enough saved up to upgrade your entire system before you worry about it.
On another note, what PSU are you using now?
If you currently have a PSU that is under 500w or has less than 30A on the +12v rail, you will need to upgrade before running this new GPU.
In this case, look into a quality Corsair, PCP&C, Seasonic or Antec Earthwatts 500w+ PSU.