The program you download is "intelligent" so it will know your resolution, and change the images to fit. My resolution is 1024x768, and everything is very crispy.
I'd suggest downloading the trial:http://starwars.screenthemes.com/
There are some great free images with it, including an absolutely astonishing Yoda closeup.
Everything is contained within the program you download, which runs in the background. You never actually download wallpaper images, just files which must be verified in the program by purchasing them. Once purchased and verified, you can choose whatever wallpaper you want, schedules to rotate the wallpapers, apply textures (like canvas and patchwork, etc) to the images, download new wallpapers, etc. When you purchase the sets, you can also purchase more credits to use towards other sets, this way you can get a bigger discount but pay more all at once.
In my opinion, worth every penny!
I've downloaded all of the classic Star Wars sets (8 in all) and got a 15% discount, so it ended up being $30.60 for 143 wallpaper images. The free download includes either 6 or 8 (cant remember) images that are also featured in other sets. They are all AOTC images, including the Yoda I mentioned above, a nice Gunship shot and some other cool shots. Lots of unique and interesting images in the purchase sets, all of which you can get a preview of on the website (in small thumbnail form).
Now I just wish Hyperspace members could get a discount!