Think of your computer like a oil pipeline. You can upgrade pumping stations all along it to increase speed in certain areas a tad, but unless you upgrade everything you'll see little improvement. What I'm getting at is that it might be worth upgrading several other components first. Notably, RAM and CPU. By doing this you avoid "bottlenecking" your entire system. I can understand if money is an issue, so here's the answer your looking for in the first place: PCI-E are all cross compatiable. The major difference is that bandwidth, or speed they transfer at. For example you look like you have a standard PCI-E 1.0 (that's first generation) for your current card.Pretty standard these days is the third generation PCI-E 3.0. Each has an increase in bandwidth. The card you will be putting into your system will run, but will run slower because it is PCI-E 2.0 in a PCI-1.0. Hopefully this makes sense. Your power should be fine. I run a power hungry card and eight core cpu on 550w so you should be alright.
