To make an online game goto file and click "new arena".
To customize a menu goto "build game" then "level settings" then press the convinent "edit" button next to the text "title screen."
To customize weapons appearences you would need a 3d animation program, but to modify range, accuarcy, ect. you can place the weapon on the level, then right click when you hover over it with your mouse.
Hope that helps!
EDIT: This would have been better if posted in product chat.
Athlon 3500 - xfx 6800XTreme - 1GB RAM - 200 GB HD
Sound card and speakers - ****