OCTGN (Pronounced Octagon) is a free, open source program designed to play cardgames online.
The first place you should head is the program's official site: www.octgn.org/. The FAQ and forums there are also invaluable if you run into problems with the program.
After you've set up OCTGN on your computer, you'll need the EVE cardpatch. Here is a zip archive containing the cardpatch and instructions on how to install it. Just open readme.txt after you've uzipped the archive.