For changing your resolution, you should take a look at your /etc/X11/xorg.conf file. I'm not using a linux machine right now, but there is a section in that file where you can edit certain display modes. Editing the display modes should allow you to choose other resolutions.
I don't know much about your WEP issue, but for WPA support you should install a program called wpa_supplicant
. Also, you may want to find out if the specific driver that you are using for this card in linux is compatible with WPA and/or WEP. If it isn't, then you should be able to install the Windows driver with ndiswrapper to get the full functionality.
I'm not sure what you're asking about the Mplayer plugin. If you're talking about the browser plugin, that is used as a way to watch embedded video files on webpages.