Hi, x4fx-
I'm not sure if this will help (I'm very new to Illustrator myself), and I'm not familiar with the cross you're referring to, but as far as symmetry goes, here's a thought: first, divide your object in half across a line of symmetry; draw half the object, then copy it (command-C), then paste it in front (command-F) - what this does is duplicates what you've drawn and pastes it exactly on top of your original. Now, go to your "Transform" palette and you'll see a little nine-point box, which allows you to choose your axis over which the duplicated image will be "flipped" (I don't know the proper term for it, but when you see it, hopefully it'll make sense.) Then go to the little arrow at the top of the palette, which will then give you a menu with the option of flipping horizontally or vertically. This will flip your duplicated piece and provide you with a perfectly symmetrical image; you can then "marry" the open points together with the join function, if you wish. If you accidentally choose the wrong axis on the 9-point box, or flip the wrong way, don't worry - just hit the "undo" function (command-Z) and you're back to where you were.
Good luck!
-Eva