For large video editing projects the prepackaged software probably won't cut it. Adobe Premiere Elements, Sony Vegas, or any one of the other popular nonlinear editing suites would be a good choice. Some editing softwares have a feature called proxy editing which will save a lot of time on a slower machine during editing. This is where reduced resolution copies of video segments are used in the editing process and replaced with the full resolution clips when the final compilation is rendered.

As for hardware, more RAM and faster CPUs will make video editing much less frustrating, especially when dealing with HD footage. I'm running an Athlon 64 X2 7755 with 8GB of ram and it still seems slow when working with HD video. Your computer should be quick enough to run most of the latest software, though I would suggest installing the maximum amount of RAM your motherboard will handle. Upgrading the processor may also be possible since the system is still relatively new.

Selecting and uploading only the best segments of footage will also help save time when working on the computer.