The format they use is called SVG, which stands for Scalable Vector Graphics. SVG files open in Adobe Illustrator, Corel Draw or the free Inkscape. They are also quite easy to modify, because the bits kind of float over the top of each other. So, for instance, click on the text on the soft drink bottle, hit delete, and type something different. Click on the lime colour and change it to strawberry red in one more click. It's easy!
To learn more about vector editing, check out some great video tutorials by Heathenx (don't be turned off by the name). The videos on his home page can be large (~40Mb), but thankfully much smaller versions are up on YouTube here. Heathenx's videos are specific to Inkscape, but the principles transfer to any vector package.
So, watch some videos, have a bit of a muck around, and you'll soon get the hang of it. Remember to save your work, and there's always the undo button if you make a mistake. Mike Pittman, Tuggeranong Presbyterian Church